Question

mendelian genetics part 1 exit ticket
identify each pedigree as autosomal recessive or autosomal dominant and explain how you determined your answer.
pedigree\tautosomal dominant or recessive\texplanation of answer
a.

b.

c.

1. mendel hypothesized that reproductive cells have only one factor for each inherited trait. this hypothesis is supported by the figure to the right showing that haploid sperm cells are produced by meiosis.

which principle of genetics does the information above support?
a. law of inheritance
b. law of segregation
c. dominant and recessive traits
d. law of independent assortment

1. chickens can have different types of feathers. frizzled feathers curl toward a chicken’s head. assume that feather type is determined by a single gene and that the allele for frizzled feathers is dominant over the allele for straight feathers. in a cross between two chickens with straight feathers, what percentage of the offspring can be expected to have frizzled feathers?
2. 0%
3. 25%
4. 50%
5. 100%

1. tomato plants usually have hairy stems. hairless stems are present in tomato plants that are homozygous recessive for this trait. if the stem characteristics are determined by a single gene, what is the expected outcome of crossing two tomato plants that are heterozygous for hairy stems?

a. 75% hairy stems: 25% hairless stems
b. 100% hairy stems
c. 100% hairless stems
d. 50% hairy stems: 50% hairless stems

Explanation:

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Question 1

Step1: Identify the genetic principle

The description states reproductive cells (gametes) get one factor (allele) per trait, which matches the law that alleles separate during gamete formation.

Step2: Match to options

The Law of Segregation explains that homologous alleles segregate into distinct gametes, resulting in haploid gametes with one allele per trait.

Step1: Define genotypes

Straight feathers are recessive, so straight-feathered chickens are homozygous recessive ($ff$).

Step2: Set up the cross

Cross $ff \times ff$. Each parent only contributes $f$ alleles.

Step3: Calculate offspring genotype

All offspring will be $ff$, so none will have dominant frizzled feathers.

Step1: Define genotypes

Heterozygous for hairy stems = $Hh$ (hairy is dominant, $h$ = hairless recessive).

Step2: Set up Punnett square

Cross $Hh \times Hh$. The Punnett square yields genotypes: $HH$, $Hh$, $Hh$, $hh$.

Step3: Phenotype ratio

$HH$ and $Hh$ (3 out of 4) show hairy stems; $hh$ (1 out of 4) shows hairless stems. This is a 75% : 25% ratio.

Answer:

B. Law of segregation

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Question 2