Chapter 1o - genes .pptx, Lecture notes of Biology

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Genes, Chromosomes, and Human

Genetics

Chapter 10

What makes you who you are?

Fig. 12-1, p. 250

1. Genetic Linkage

Genes

• Sequences of ____________ in DNA
• Arranged __________ in chromosomes

Do all genes assort independently?

In Mendel’s work ___ 7 characters assorted

independently, however this is ______ for all

genes.

• (^) Some genes are ________ together. Why?

  Because they are on the same ___________  LINKED GENES



Drosophila melanogaster

Fruit fly

• Model organism for animal genetics
• Compared to Mendel’s peas
• Morgan - first genetic map
• Used to test ______ and ___________  Based on how far apart genes are on a chromosome

Remember - Crossing-Over

Fig. 10-14, p. 220 Closer 2 genes are the more linked they are because less chance of crossing over between them.

Genetic Recombination

Alleles linked on same chromosome

exchange segments between __________

chromosomes

Exchanges occur while homologous

chromosomes pair during _______________

Experimental Evidence for Gene Linkage Fig. 12-2, p. 252

Dihybrid Testcross

P Generation

Rr Yy × rr yy

• (^) F 1

Generation

¼ = round yellow ¼ = round green ¼ = wrinkled yellow ¼ = wrinkled green

1:1:1:1 ratio

Principle of __________________

Recombination Frequency

Amount of recombination between two genes

reflects the _______ between them

The greater the distance, the greater the

_______________________

• Greater chance of crossover between genes

Linkage Maps of Chromosomes

• (^) Recombination frequencies used to determine ____________ on a chromosome
• _______________ for genes a , b , and c :
• (^) 1 map unit (1 centimorgan) = 1% recombination

Single and Double Cross Overs

A a C c B b

X

Single Cross-over A a C c B b

X X

Double Cross-over a C b A c B A C c B b a

Can genes on the same chromosome

ever assort independently?

Widely separated

linked genes often

recombine

• Seem to assort independently
• (^) Detected by testing linkage to genes between them Fig. 12-5, p. 254 ______ recombination frequency = __________ assortment

Why only 50% max?

Fig. 10-14, p. 220 Recombination only between 2 of 4 chromatids. Only half gametes will have recombined chromosomes.