Mendelian Genetics

Topics: Allele, Sex linkage, Genetics Pages: 3 (470 words) Published: April 10, 2013
Punnet square: dihibyrid cross- 2 parents w/2 different traits
Ex: seed shape & seed color

Cross pure-lines
2. F1 offspring are all heterozygous,
Cross F1 x F1
F2 generation shows individuals of both phenotypes, in a specific ratio 9:3:3:1

-this would only occur if independent assortment = 2 alleles separate & sort independently into gametes

Rules of inheritance
Different alleles for the same gene
Principle of segregation-each gamete has 1 allele of each gene Principle of independent assortment
Results in patterns of inheritance by Mendel
Meisois 1 is during which segregation occur and principle of ind. Assortment occurs

Linked Genes
X-linked trait (or sex-linked)
Found on the X chromosome
Why important?
In males → x-linked traits are often expressed, because have only 1 x=chromosome. And no corresponding gene on the Y-chromosome In females → if X-linked trait is recessive → masked by dominant allele on other chromosome (females are carriers for the trait)

Linked genes
-two or more genes found on the same chromosome
-if the genes are linked, they would always be transmitted together but this violates the principle of independent assortment If recombination(crossing over) occurs, principle of independent assortment is not violated Recombination – combination of alleles on the offspring chromosome in the gametes are different from the combination of alleles present in the parents Cross-over occurs during Prophase I

At least 1 time per pair of homologous chromosomes
-if recombination occurs, principle of independent assortment is not violated the distance between genes determines the frequency of crossing over, close together, cross over rare, far apart it is frequent Genetic Maps

20% of the offspring are recombinant, the two genes are 20 map units apart how many map units on chromosome -----
How often does this occur?
If genes are more than 50 map units apart they will sort independently Cross over...
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