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Flashcards in chromosome behaviour during cell divisions Deck (19):
1

what occurs in each of the following sections of prophase I: leptotene, zygotene, pachytene, diplotene

leptotene: chromosomes start to condense
zygotene: homologous chromosomes become closely associated to form pairs of chromosomes consisting of 4 tetrads
pachytene: crossing over between pairs of homologous chromosomes to form chiasmata
diplotene: homologous chromosomes continue to separate but remain attached by chiasmata

2

what is meant by the term 'cross'?

the fusion of male gametes from one individual and female gametes from another

3

define 'monohybrid cross'

crosses between true breeding strains with alternative forms of a single trait

4

what information does a reciprocal cross give you?

whether inheritance of a trait depends on sex

5

what is Mendel's principle of segregation?

alleles separate from eachother during the formation of gametes in meiosis

6

what is meant by product rule?

the probability of two interdependent events occurring simultaneously, the product of each of their individual probabilites

7

what is meant by sum rule?

the probability of occurance of any mutually exclusive events is the sum of the probability of individual events

8

what is the Chi-squared test used for?

to determine whether a difference is due to chance, and if the null hypothesis should be rejected

9

what is meant by complementation?

when 2 strains of an organism with different homozygous recessive alleles produce offspring with wild-type phenotype when crossed

10

why does linkage happen?

alleles on the same chromosome will not assort independently and will co-segregate at meiosis

11

what indicates linkage?

greater observed number of parental phenotypes than recombinants or by RF <50%

12

how is RF calculated?

total recombinants/total progeny x100

13

what causes RF to reach 50%?

one or more chiasmata between 2 genes in every meiosis

14

what does a dominance test test?

studies the phenotype of the heterozygote F1; the functional relationship of alleles on the same gene

15

what does a complementation test study?

the phenotype of F1, tests the functional relationship of two recessive mutations

16

what are the characteristics of an autosomal recessive disease?

-heterozygotes unaffected
-2 heterozygotes have 25% chance of having affected offspring
-2 homozygous individuals will have affected offspring only
e.g: cystic fibrosis

17

what are the properties of an autosomal dominant disease?

-every affected individual has 50% chance of having affected offspring
-disease cannot skip generations
-e.g. Huntington's disease

18

what are the properties of an X-linked recessive disease?

-hemizygous males and homozygous females affected
-female carriers have 50% chance of having affected sons
-affected males cannot give traits to sons
-e.g. Haemophilia A

19

what are the properties of an X-linked dominant disease?

-hemizygous males and heterozygous females affected
-affected male cannot give trait to sons but gives it to his daughters
-focal dermal hypoplasia