Unit 8 Meiosis and MendelGenetics and Inheritance

Quiz Date: Jan 14

Test Date: Jan. 22/23

UNIT 8 - INTRODUCTION TO GENETICS

• Although the resemblance between generations of

organisms had been noted for thousands of years, it

wasn’t until the 1800s that scientific studies were

carried out to develop an explanation for this. Today

we know that we resemble our parents because of

_______________, which is the set of characteristics

we receive from ______________________. The

study of heredity is known as _________________.

heredityour parents

genetics

I. SEXUAL REPRODUCTION & MEIOSIS (pp. 275-278)

• In sexual reproduction, an egg and sperm cell

fuse together to create a fertilized egg or

_______________. zygote

A. Chromosome Number

1. Somatic Cells - _____________ cells•Human somatic cells contain ________ chromosomes•______________ or ________ meaning they contain a ____________ set of chromosomes, half ( _____ ) from _________ and half from ________. •“Matching” chromosomes known as ____________________.

•made up of a copy of a chromosome from each parent, with the same ___________, but they are ____________________.

•Somatic cells use ___________ for growth, development, renewal, and repair

Body46

Diploid 2ndouble 23Dad Mom

Homologous pairs

genes not identicalmitosis

Homologous Chromosomes

GAMETES

2. Gametes - ___________ and _______________

cells

• Human gametes contain ______ chromosomes.

• ______________ or ______ meaning there is

_____ set of instructions for each ______.

• When gametes fuse together in

_____________________, the ________________

produced is _____________ and has _______

chromosomes.

• Gametes are produced by a process called __________, rather than mitosis

Egg Sperm

23Haploid n

one gene

fertilization zygotediploid 46

meiosis

Haploid vs. Diploid

Karyotypes

B. Meiosis

• Special type of cell division that only occurs in

specialized germ cells (sex cells) in ____________

of females and ______________ of males.

• Before meiosis, DNA is replicated once (during

______ phase of ________________)…

• …But during meiosis cell divides

________________, resulting in ______ cells with

_______ the original chromosome number.

• Unlike mitosis which produces identical cells, meiosis produces genetically _____________ cells.

ovariestestes

2X, two times 41/2

S interphase

non-identical

Identical somatic cells Unique gametes

• Meiosis occurs in two stages:

1. Meiosis I

Prophase I➢Unlike in prophase of mitosis, In prophase I

___________________________ come together and

stick to each other to form a ______________.

Homologous pairstetrad

Meiosis I➢Crossing Over

▪ Exchange of genetic information between a

________________________________ with its

___________________________________.

▪ Occurs very frequently

▪ Allows for __________________________.

Sister chromatidNon-sister homologue

Genetic variation

Meiosis IMetaphase I

➢_____________________________ align in equator of cell

➢Each homologue consists of _______________________________________.

Anaphase I➢__________________________________________ are

pulled apart➢_________________, _________________________

still intact

Tetrads

Two sister chromatids

Homologous pairs

Centromeres Sister chromatids

Meiosis I Telophase I

➢Two cells are formed, each with _______ chromosomes

➢Each chromosome still composed of two

___________________

➢Two cells produced at the end of meiosis I are

_______________ because______________________

23

Sister chromatids

haploid There are no homologous pairs present

MEIOSIS II

2. Meiosis II

Prophase II

Continues with the two cells formed moving directly

into prophase II without any further

_____________________ of DNA.

Metaphase II

_______________ (not tetrads) composed of

__________________ are randomly aligned at the

equator of the cell.

replication

Chromosomes

Sister chromatids

2. Meiosis II

Anaphase II

Spindle fibers shorten

______________________ are pulled apart, just

like in anaphase of mitosis.

Telophase II

Four nuclei form around chromosomes, spindles

break down

Sister chromatids

2. Meiosis II

Cytokinesis II

Two new cells are formed from each of the two cells

formed in meiosis I, resulting in a total of

___________ new cells, each with

____________the original number of

chromosomes.

Cells produced are called ____________________.

41/2

Gametes

MEIOSIS

• In females, process is known as

________________________.

• In males, process is known as

_________________________.

oogenesis

spermatogenesis

3. Oogenesis vs. spermatogenesis

• Spermatogenesis: Males produce 4 viable sperm cells

• Begins:

____________

• Ends:

___________

puberty

death

3. Oogenesis vs. spermatogenesis

• Oogenesis: Females produce only one egg and 3 polar bodies

• Begins:

___________

• Ends:

___________

Before birth

menopause

Spermatogenesis vs Oogenesis

II. HISTORY OF GENETICS (pp. 263-270)

• A. Gregor Mendel

• Known as the “Father of _______________”• Famous for his experiments with ________ plants.

Geneticspea

Mendel• Used true-breeding pea plants, which means

________________________; characteristics

always show. Known as the ____________

generation.

• Studied seven ______________, including plant

height, seed color, flower color, etc. o A character is an ______________________________.

o A trait is a variant of a character

o Example: Eye color is a character, brown eyes or blue

eyes are traits

pureline, purebredP

characters

Inherited characteristic

Mendel

• Pea plants cross-pollinate, meaning pollen from

one plant fertilizes an egg from another, but they

can also self-pollinate, meaning pollen can fertilize

egg from ______________ plant. Mendel

controlled the fertilization process of the pea plants

by preventing

__________________________________ and

controlling

___________________________________.

same

Self-pollination

Cross-pollination

Pea Traits Studied

•

B. Mendel’s Results

• P generation – Crossed __________________ plants with one trait with ________________ plants with the other.

• For example, _____________________________________________

• F1 generation – Offspring produced from _________________. In F1, one trait ____________. For example, tall plants X short plants = __________________________.

• F2 generation – Offspring produced from _________________. In F2, trait that disappeared in F1reappeared in __________ of the offspring; the other ¾ showed _____________________________.

True-breedingTrue-breedingTT (tall) x tt (short)

P X P disappeared

All tall plants

F1 X F11/4

Dominant trait

•

Mendel’s Principles

• C. Mendel’s Principles – After analyzing his

results carefully, Mendel formed conclusions that

increased understanding of inheritance and opened

the door for the study of genetics.

• Individual units called ___________ determine

inheritable characteristics. A gene is a portion of

___________ that codes for a specific ____________.

genes

DNAtrait

Alleles and Genes

Mendel’s Principles

• For each gene, an organism inherits two alleles, one from each __________________. Alleles are different forms or ____________________ of a ___________. For any given trait,o If an organism is ___________________ (for a gene), its alleles

are the same and the trait will be expressed.o If the alleles differ, the organism is said to be

___________________ for that character and only one allele will be expressed. The expressed allele is the ______________ allele, designated by an __________-case letter. The allele that is not expressed in a heterozygous trait is _________________, designated by a _____________-case letter. A recessive allele is only expressed when an organism is ________________ for that gene.

parentversions gene

homozygous

heterozygousdominant

upperrecessive

lowerhomozygous

Mendel’s Principles

• Principle of Segregation - In meiosis, the two alleles for a trait segregate (_______________). Each egg or sperm cell receives a copy of one of the two alleles present in the somatic cells of the organism. There is a _________ chance that a copy of that allele will end up in the gamete produced.

• Principle of Independent Assortment – The way one pair of alleles segregates has no influence on any other pair of alleles.

separate

50%

Independent Assortment

D. Genetics Terminology

• 1. Phenotype - ________________ description of

trait; for example, ______________

• 2. Genotype – Genetic make-up of an organism or

set of alleles; for example, ____________________.

Physical

Tall, short

TT, Tt, heterozygous, etc..

Genetics Terminology

• 3. Application of Terminology - If round pea seeds are dominant to wrinkled pea seeds, round is designated _____ and wrinkled is designated ______.• a. Homozygous dominant• Genotype = ________; Phenotype = ________• b. Heterozygous• Genotype = ________; Phenotype = ________• c. Homozygous recessive • Genotype = ________; Phenotype = ________

Rr

RR round

Rr round

rr wrinkled

III. ANALYZING INHERITANCE (pp.135-137)

• A. Probability

Due to the law of_______________, if you know the

genotype of the parents, you can predict the likelihood

of a trait occurring in the offspring. Probability can be

written 3 ways. The probability of a coin coming up

heads after being flipped is (fraction) _____, (ratio) ________, or (percent) _______.

segregation

1/21:1 50%

B. Punnett Squares• A Punnett square is a tool used to predict the

possible outcomes of _______________ and

____________________; in other words, a Punnett

square is used to determine the probability of certain traits appearing in offspring.

meiosisfertilization

Punnett Practice Monohybrid crosses A-D

• Must have a key

• And Cross with

• Each problem

• For full credit

A: Construct a Punnett square to determine the probability of white flowers is a heterozygous purple

flower (Pp) is crossed with a homozygous white flower (pp)

1. Key:________________________

2. Cross:________________

Probability of White flowers:___________50%

P=purple, p=white

Pp X pp

P p

p

p

Pp pp

Pp pp

B: Construct a Punnett square to determine the probability of short pea plants if a homozygous tall

plant (TT) is crossed with a heterozygous tall plant (Tt)

1. Key:__________________

2. Cross:________________

Probability of short pea plants:___________

Probability of tall pea plants:___________

T=tall, t=short

TT X Tt

T T

T

t

TT TT

Tt Tt

0%

100%

C: If round peas are dominant over wrinkled peas, make a Punnett square to determined the genotype

and phenotype ratios of the offspring if a heterozygousplant is crossed with a homozygous recessive plant

1. Key:__________________

2. Cross:________________

R=round, r=wrinkled

Rr X rr

R r

r

r

Rr rr

Rr rr

RR:Rr:rr 0:2:2

2:2

Genotypic ratio:__________________

Phenotypic ratio:_________________

D: Use a Punnett square to determine the genotype and phenotype ratios of the offspring from a cross

between a homozygous dominant yellow pea plant and a homozygous recessive green pea plant

1. Key:__________________

2. Cross:________________

Y=yellow, y=green

YY X yy

Y Y

y

y

Yy Yy

Yy Yy

YY:Yy:yy 0:4:0

4:0

Genotypic ratio:________________

Phenotypic ratio:_________________

Dihybrid crosses

The punnett squares we have been doing are known as ____________________ crosses, meaning that only one traits has been considered at a time. In a dihybrid cross, __________ different ______________ on 2 different _____________ are analyzed.

monohybrid

2

genes

chromosomes

Punnett Practice dihybrid crosses A-B

1. Key

2. Cross

3. Punnet square

A. Peas homozygous for round shape and heterozygous for color are crossed with

heterozygous yellow peas, heterozygous for shape

Key: R=round, r=wrinkled

Y=yellow, y=green

Cross: _____________________

Genotypic

ratio:_______________________

___________________________

_________

Phenotypic ratio:

___________________________

__________________________

B. Key: G= gray body, g= black body;

R=red eyes, r =black eyes

Cross: GGRr X Ggrr

What are the phenotypes of the

parent fruit flies:

___________________________

________________________

Genotypic ratio:

___________________________

________________________

Phenotypic ratio:

___________________________

__________________________

Incomplete Dominance

• Neither allele has “complete” dominance over the other; heterozygous phenotype is a blendof the 2 homozygous phenotypes

• Ex: snapdragons

R = red

W = white

RW = pink

Incomplete Dominance: cross a pink snapdragon with a white snapdragon

1. Key: _________________________

2. Cross: ________________________

Phenotypic ratio:___________________

Genotypic ratio:____________________

Incomplete Dominance: cross a red snapdragon with a white snapdragon

1. Key: _________________________

2. Cross: ________________________

Phenotypic ratio:___________________

Genotypic ratio:____________________

Codominance• Codominance – Both alleles share dominance and

are always expressed if present.

• Ex: In chicken

B = black feathers

W = white feathers

BW = black AND white

feathers

X

Codominance: cross a black chicken with a black and white chicken

1. Key: _________________________

2. Cross: ________________________

Phenotypic ratio:___________________

Genotypic ratio:____________________

Codominance: cross a white chicken with a black and white chicken

1. Key: _________________________

2. Cross: ________________________

Phenotypic ratio:___________________

Genotypic ratio:____________________

Polygenic Traits

• “Many genes” ; Many traits are controlled by more than one gene; have a variety of choices for expression.

• Ex: _hair color, eye color, skin tone

Multiple Alleles

• Many genes that have more than 2 alleles, although an individual only has 2 alleles for the gene.

• Ex: blood group.

• There are 3 possible

• alleles for this gene.

Suggested study questions

• p. 283 (1-5, 11, 12, 17-20)