Genetics

Traits

➢ Inherited – individual characteristics that are passed from one generation to the next; from parents to offspring.

– Eye, hair, skin color,...

➢ Acquired – characteristics that are learned from the environment.

– How to walk, talk, write, act,...

Genes

➢ Specific sections located on your chromosomes.

➢ Control your inherited traits.

➢ You get one gene from each parent for every trait you have.

Types of Genes

➢ Genes that show up more often in nature (“stronger”) are referred to as DOMINANT.

➢ Represented by a CAPITAL LETTER (ex. T is for tall)

➢ Genes that show up less often in nature (“weaker”) are referred to as RECESSIVE.

➢ Represented by a lower case letter (ex. t is for short)

Genotype➢ Alleles – variations of genes

➢ Genotypes are the 2 alleles that you receive from each parent for each trait you have.

➢ Your genotype CANNOT be changed.

➢ It is coded on your DNA

➢ This is expressed with letters.

➢ Homozygous = both alleles received are the same

➢ 2 dominant alleles = TT

➢ 2 recessive alleles = tt

➢ Heterozygous = each allele received is different

➢ 1 dominant and 1 recessive = Tt

Phenotype

➢ Phenotypes are the outward expression of your traits. It is based on the genotype.

➢ Your phenotype CAN be changed.

1. Two dominant alleles (TT) show the dominant trait = tall plant

2. Two recessive alleles (tt) show the recessive trait = short plant

3. One dominant & one recessive allele (Tt) show the dominant trait = tall plant

Genotype and Phenotype

Punnett SquaresPunnett Squares are used to determine the probability of a trait being passed from parent to offspring.

Black fur (B) is dominant over brown fur (b) in rabbits.

Use the Punnett Square

to predict the genotypes

and phenotypes of the

offspring of two rabbits

that are heterozygous (Bb)

for hair color (black).

Bb x Bb

D

MB b

B

b

BB

Bb

Bb

bb

Genotypes

_______ _____%

_______ _____%

_______ _____%

Phenotypes

___________ %____

___________ %____

Brown dominant eye color

1.My parents both have blue/green eyes.

2.Is this dominant or recessive?

3.What is the probable genotype of my parents' for eye color – using the letter b for the trait?

4.How many genotypes are possible for my brother and me?

5.What is it?

6.My husband has brown eyes, and both his parents have brown eyes. What are their probable genotype(s)?

7.Matthew has brown eyes and Nathan has blue eyes. What is the genotype for each of them?

8.Can my husband’s genotype be BB? Why or why not?

My Dadbb

Mark's mom

Bb (or BB)

Mark's dad

BB (or Bb)

MarkBb

Nathanbb

MatthewBb

Mebb

My Mombb

bb

bb b

b

B

BB = dominant

Brown eye

b = recessive

Blue eye

Homozygous recessive = My dad,my mom, me and Nathan Homozygous dominant = Mark’s

dad or mom

Heterozygous dominant = Mark’s mom or dad, Mark and Matthew

Mendel's Laws of Genetics1st Law – Law of Segregation

➢ During meiosis, the 2 alleles (genes) responsible for a trait separate from each other.

➢ When the egg and sperm unite in fertilization, those 2 alleles (genes) are recombined, producing a genotype in the offspring for that trait.

1st generationAll Tall

2nd generation75% Tall; 25% short

T T T t

Tt Tt TT Tt

Tt Tt Tt tt

t

t

T

t

22ndnd Law – Law of Dominance Law – Law of Dominance

➢ Mendel discovered that for every trait there is a DOMINANT allele (gene) and a RECESSIVE allele (gene).

➢ When pure parents are crossed, the Dominant trait shows up. TT x tt = Tt (tall)

➢ Hybrids always show the Dominant trait.

➢ The only way for a Recessive trait to appear is to receive 2 Recessive alleles (genes); one from each parent. (tt = short)

33rdrd Law – Law of Independent Law – Law of Independent AssortmentAssortment

➢ Different traits are inherited independently of one another.

➢ For example: If you inherit blue eyes, that does not mean you will inherit blonde hair.

Dihybrid cross = parents are hybrids for 2 different traits.(Makes a big Punnett Square) RrGg x RrGgR = round seeds; R = round seeds; r = wrinkled r = wrinkled G = green pods; G = green pods; g = yellowg = yellow

RG Rg rG rg

RG RRGG RRGg RrGG RrGg

Rg RRGg RRgg RrGg Rrgg

rG RrGG RrGg rrGG rrGg

rg RrGg Rrgg rrGg rrgg

Codominance

• a cross between parents

with two different

phenotypes produces

offspring with a third

phenotype in which both

of the parental traits

appear together.

brown x black ---> brindle

BB x KK 100% BK

Incomplete Dominance

• a cross between

parents with two

different phenotypes

that produces

offspring with a third

phenotype that is a

blending of the

parental traits.

RED Flower x WHITE Flower ---> PINK Flower

RR x rr 100% Rr

Codominance or Incomplete Dominance?

PedigreePedigree

Females Males

Similar to a family tree, but is used specifically to analyze or predict the inheritance of a trait over many generations, specifically family diseases. https://www.youtube.com/watch?v=Wuk0W10EveU

NeurofibromatosisCystic Fibosis

CHILD Syndrome

Hunter Syndrome

Hemophilia – bleeding disorder