genetics 137

Genetics

Vocabulary Review Allele Dominant vs. Recessive Heterozygous vs. Homozygous Phenotype vs. Genotype

Law of Segregation allele pairs separate or segregate during gamete

formation, and randomly unite at fertilization.

Monohybrid Crosses (Punnett Squares)

Genotype Ratio?1AA:2Aa:1aa

Phenotype Ratio?3dominant:1recessive

Punnett Squares Things to consider:

Which trait is dominant and which is recessive? Is each parent heterozygous or homozygous (dominant

or recessive)? What allele abbreviation would we use? Genotype and Phenotype ratios can be DIFFERENT!!!

Molly and Neil are planning to have children. Molly has blue eyes and Neil has brown eyes. What color eyes could their children have?

**Neil’s mom had blue eyes and his dad was homozygous for brown eyes**

Now we know:Molly=bbNeil=Bb

Genotype Ratio:1Bb:1bb

Phenotype Ratio:1 brown eyes: 1 blue eyes

In plants, tall height (T) is dominant to short (t). A homozygous dominant plant is crossed with a heterozygous plant. What would be the resulting phenotypic and genotypic ratios in the resulting generation of plants?

Incomplete Dominance form of intermediate inheritance in which one allele for a specific

trait is not completely dominant over the other allele resulting in a third phenotype that is a combination of the dominant and recessive phenotypes

Genotypic Ratio? 1:2:1 (WW:RW:RR)

Phenotypic Ratio? 1:2:1(white:pink:red)

Sex-linked Traits (Examples: red-green color blindness, hemophilia) xBxB : normal female xBxb: carrier female xbxb :affected female xBy: normal male xby: affected male

Cross a male with hemophilia with a normal woman whose father had hemophilia.

xHXh xHy

Xh Xh Xhy

Xh y

xH

Xh

Genotypic ratio: 1xHXh

:1xHy: 1Xh Xh : 1Xhy

Phenotypic ratio: 1 normal female: 1 hemophiliac female: 1 normal male: 1 hemophiliac male

Review Questions A male with hemophilia marries a normal woman whose

father had hemophilia. What are the chances of their sons and daughters having hemophilia? Be sure to give the phenotypic and genotypic ratios.

A normal male marries a woman who is also normal but whose father was colorblind. What are the chances of their sons and daughters being color blind? Give the phenotypic and genotypic ratios.

Blood Type: Multiple Alleles Blood types: A, B, AB, and O

Alleles Codominance: A & B I A and IB (can be homozygous or heterozygous)

Recessive: O i

A female with type AB blood is crossed with a man who has type O blood. What are the genotypic and phenotypic combinations their children could have?

Parents: I AIB x ii I A IB

Genotypic Ratio: 1 I A i: 1 I B i Phenotypic ratio: 1 type A: 1 type B i

i

I A i I B i

I A i I B i

*Look over dihybrid cross notes*

END PUNNETT SQUARES

Pedigrees: chart of an individual's ancestors used in human genetics to analyze Mendelian inheritance of certain traits, especially of familial diseases.

Pedigrees

Female Male Offspring

Pedigrees

Female with specific trait Male with specific trait

Individuals can be shaded to track certain traits.

Pedigree Key:

& = color blind

& = normal vision

What would be the genotype of each of the individuals? xbxb

xBxb xby

xBy