Biology Chapter 11 Introduction to Genetics Genetics: The scientific study of heredity Heredity –...
-
Upload
arlene-adams -
Category
Documents
-
view
224 -
download
1
Transcript of Biology Chapter 11 Introduction to Genetics Genetics: The scientific study of heredity Heredity –...
Biology Chapter 11 Introduction to Genetics
Genetics: The scientific study of heredity
Heredity – the passing of traits from parents to offspring
Inheritance
• You get your genes from your parents
• In meiosis, half of the chromosomes in a pair come from the Dad, half come from the Mom
• What we know today is based on the work of Gregor Mendel – Austrian monk
Key terms to know
• Allele – each form of a gene for a certain trait (R or r)
• Gene – sequence of DNA that codes for a protein a thus determines a trait
• Genotype – combination of alleles for a given trait ( RR or Rr or rr)
• Phenotype – Appearance of trait ( round seeds or wrinkled seeds
Terms continued
• Homozygous - when you have 2 or the same alleles for a given trait (RR or rr)
• Heterozygous – when you have 2 different alleles for a trait (Rr)
• Incomplete dominance – blending of alleles to produce a different phenotype (red and white produce pink)
• Codominance – Both alleles are expressed equally (produces combinations of each- red and white produce red spotted white)
• Multiple alleles – a set of 3 or more different alleles controlling a trait ( eye color, skin color)
Gregor Mendel
• Born in 1822 in Czech Republic
• Became a priest and studied math and science at the University of Vienna
• Worked for next 14 years in the monastery as head of monastery garden and taught at the high school
Mendel studied seven/eight different pea plant traits…
• Trait – a specific characteristic that varies from one individual to another
(ex. Seed color, height, hair color)
• Mendel’s studied traits had two contrasting characters or “alleles” -- different forms of a gene
Seed Shape
Flower Position
Seed CoatColor
Seed Color
Pod Color
Plant Height
PodShape
Round
Wrinkled
Round
Yellow
Green
Gray
White
Smooth
Constricted
Green
Yellow
Axial
Terminal
Tall
Short
Yellow Gray Smooth Green Axial Tall
Section 11-1
Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants
Go to Section:
see page 310 in textbook
Seed coat color and flower color are often put in for one another – thus, the EIGHT traits!!!
*Flower color – purple (P) vs. white (p)
Mendel’s test crosses….
• Testcross: experimental cross between an individual with the dominant phenotype for a given trait (genotype unknown, though) and another individual with the recessive phenotype (homozygous recessive)
• P1 generation – parents that Mendel cross-pollinated
• F1 generation – offspring of P1 that were allowed to self-pollinate
• F2 generation – offspring of F1 generation
Mendel’s Conclusions….
• Biological inheritance is determined by “factors” that are passed from one generation to a next – today, called genes
• Law of Dominance: where there are two or more forms of a gene for a single trait, some alleles are dominant and other alleles are recessive
• Law of Segregation: alleles segregate (separate) from each other during the process of meiosis (gamete formation)
• Principle of independent assortment: genes for different traits can segregate independently during the formation of gametes
concluded that
which is called the
which is called the
GregorMendel
Law ofDominance
Law ofSegregation
Peaplants
“Factors”determine
traits
Some alleles are dominant,
and some alleles are recessive
Alleles are separated during gamete formation
Section 11-3
Concept Map
Go to Section:
experimented with
Principle of Independent Assortment
This one follows from the law of segregation – all alleles are not permanently associated with one another….
Punnet Squares
• Used to predict the possible gene combinations for a a cross
• Traits are represented by letters– Lower case letters = recessive traits– Upper case letters = dominate traits
How to do punnett squares
1. determine the genotypes of the parent organisms 2. write down your "cross" (mating) 3. draw a p-square 4. "split" the letters of the genotype for each parent & put them "outside" the p-square 5. determine the possible genotypes of the offspring by filling in the p-square 6. summarize results (genotypes & phenotypes of offspring) 7. bask in the glow of your accomplishment !
Links to punnet square practice
• http://www.athro.com/evo/gen/punexam.html
• http://biology.clc.uc.edu/courses/bio105/geneprob.htm
1. Give at least three examples of traits that humans can inherit from their parents.
2. Imagine that you have attached earlobes, which is a recessive trait (represented by the lowercase letter r). You want your offspring to have free earlobes (represented by the uppercase letter R). What is the ideal genotype of your mate for this situation and what is the probability that your offspring will have your desired phenotype?
Warm-up
Draw two Punnett squares to figure out the following situation.
Two pea plants, one yellow and one green, are bred together that are homozygous for pod color. The dominant trait is yellow (Y) and the recessive trait is green (y). The offspring of these two pea plants are then bred together. What are the chances of the third generation having each phenotype?
• Besides straight dominant and recessive genes, two other possibilities for combinations were proven:
Codominance: when 2 alleles work together and BOTH are expressed without one masking the other
Multiple Alleles: when more than two possibilities for a trait are present.
• Example: Blood typeThere are 3 alleles for blood type -- A, B, O
Possible combinations:AA, AO -- Type A bloodBB, BO -- Type B bloodAB -- Type AB
bloodOO -- Type O blood
• Here, A and B are dominant over O, but if A and B are present together, neither dominates!!! This is codominance – they share the power of expression.
• Incomplete Dominance: when BOTH alleles in an individual affect the appearance of a trait and you get a brand new color that was not found in the original parents. Both traits are written in capitals and have different letters because BOTH control the appearance.
• Example: flower color in snapdragons
Pure red (RR) X Pure white (WW)
Humans are difficult to study…
Why?1. # of human genes is extremely large (each cell
has ~100,000 different genes)2. Humans cannot be easily controlled by an
investigator3. Time span between generations is long4. Only a small # of offspring are produced by
each set of parents5. Environment has a HUGE effect on a person’s
development…
Have developed ways to approach the difficulties…
• Pedigree analysis – family history for a particular trait
See page 315-316 for example
• Study of Genetic diseases
• Twin studies – Nature vs. nurture
• Population Sampling
• Genetic Technology
Errors in chromosomes…
1. Mistakes in numbers of chromosomes:
nondisjunction -- members of a pair of homologous chromos do not move apart properly
result in offspring that have
Aneuploidy – abnormal chromo number
Trisomy or Monosomy or Polyploidy
2. Mistakes in shape of chromos:a. deletion – part of chromo is broken off and lost
completelyb. duplication – broken fragment of chromo
attaches to sister chromatid so section is repeated on that chromatid
c. inversion – when fragment reattaches to original chromo but in reverse order
d. translocation – broken fragment attaches to a nonhomologous chromo(can exist as reciprocal or nonreciprocal)
Genetic Technology
• Carrier recognition with genetic screening and Fetal testing
-ultrasound and sonograms
-amniocentesis
-chorionic villi sampling
-fetoscopy
-blood/urine tests of newborns