Inheritance of linked genes

• Biologie
• Middelbare school
• vwo
• Leerjaar 4

Inheritance of linked genes

T4

Genetics

Learning Objectives

- You know the difference between independent and linked inheritance in dihybrid crosses

- You recognize whether a dihybrid cross inherits independently or in pairs

- You can work out linked, dihybrid crossings systematically.

Types of crossings: what should I be able to do?

MONOHYBRID

regular

incomplete / co-dominant

multiple alleles

lethal factors

X-chromosomal

DIHYBRID

any combination of the two above types

independent

linked

Linked inheritance

Both genes are on the SAME

chromosome

Independent inheritance

Both genes are on DIFFERENT

chromosomes

Notation of Linked Inheritance

Because the alleles are literally 'linked' in linked inheritance, they are passed on to the offspring in fixed combinations. There is therefore less variation in gametogenesis (formation of sperm / egg cells).

It is very important that the alleles on the same chromosome are noted as such.

So use the following notation -->

In fruit flies, the allele for gray body color (G) is dominant over the allele for black body color (g). The allele for normal wings (N) is dominant over that for wing stumps (n). Both genes are located on the same chromosome. A gray female with normal wings, homozygous for both traits, is crossed with a black male with wing stubs (vleugelstompjes).

Give the genotypes of the female, male and of the F1 generation. Use the correct notation!
Also provide the corresponding Punnett square.

The F1 is mutually crossed.
Give the phenotype ratio of the F2.

A heterozygous male is crossed with a black female with wing stubs.
What genotypes can the male have? Use the correct allele notation!

How can you determine which alleles of both genes are co-located on a chromosome (haplotype) if an individual is heterozygous for both linked genes?

P. heterozygous male x black female with wing stumps.

F1. 48x gray flies with normal wings
51 x black flies with wing stubs.

What haplotypes did the P. generation male fly have? Support your answer with a Punnett square.

What is the phenotype ratio in the F1. generation if in the 'father fly' the dominant G allele was linked to the recessive n allele (so has the other haplotypes)?

Substantiate your phenotype relationship by means of a crossing scheme.

Learning Objectives

- You know the difference between independent and linked inheritance in dihybrid crosses

- You recognize whether a dihybrid cross inherits independently or in pairs

- You can work out linked, dihybrid crossings systematically.

Work to be done

Biozone 153 (Inheritance of linked genes), Handout: Dihybrid crosses – 2 problems with linked alleles.  Biozone154 (Recombination and Dihybrid inheritance). Handout – Three problems illustrating no linkage, linkage and linkage with crossing over.  Assessment Questions Glencoe pg 320: Q 21-27 + 29