Standard 2.2 Molecular basis of inheritance A sorting and recombination of genes during sexual reproduction results in a great variety of possible gene combinations from the offspring of any two parents (i.e., Punnett squares and pedigrees). Students will understand concepts in a single trait cross (e.g., alleles, dominant trait, recessive trait, phenotype, genotype, homozygous, heterozygous, incomplete dominance, and sex-linked traits).

Section 10.1 Summary – pages The rule of dominance An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele. The dominant allele is always written first…rule of ? TT T T tt t t All tall plants F1F1 Tall plant Short plant 42

3

4

5

Section 10.1 Summary – pages A Punnett square for this cross is two boxes tall and two boxes wide because each parent can produce two kinds of gametes for this trait. Monohybrid crosses Heterozygous tall parent Tt T t Tt T t Heterozygous tall parent Tt T t TTTt tt 43

1:4 or 25% and millimeters is length while grams is measuring mass

8

9 17. In a certain group of lab mice black fur is dominant and brown fur is recessive. If two heterozygous mice mate and produce 16 offspring, how many of the offspring will probably have brown fur? A 0 B 4 C 8 D 12

10

11

12

Incomplete Dominance appearance of a 3 rd phenotype. Example: A homozygous red-flowered plant (RR) is crossed with a homozygous white-flowered plant (R’R’), all of the F1 generation offspring will have PINK flowers (RR’). RR’ R R R’ 45

14

Codominance Expression of both alleles Example: Black (BB) rooster crossed with a white (WW) hen = checkered (BW) black and white. (Incomplete dominance would have been gray!) 46

The 23 rd pair of chromosomes in humans are ___ ____________and determine the sex of the offspring. XX = female XY = male 47 sex chromosomes

Traits controlled by genes located on sex chromosomes sex-linked traits 48

Traits controlled by more than 2 alleles have this… multiple alleles Example: Pigeons have 3 alleles that control feather color. B A = ash red B = blue b = chocolate 49

Polygenic inheritance pattern of a trait that is controlled by 2 or more genes. Example: eye color, skin color, height (AaBbCc…) 50

21

Pedigree graphic of genetic inheritance = Male = Female = affected Male = affected Female = Mating = Parents = Siblings = known heterozygous “carriers” = Death 51