chromosome behaviour during cell divisions Flashcards Preview

Genes > chromosome behaviour during cell divisions > Flashcards

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

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


what is meant by the term 'cross'?

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


define 'monohybrid cross'

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


what information does a reciprocal cross give you?

whether inheritance of a trait depends on sex


what is Mendel's principle of segregation?

alleles separate from eachother during the formation of gametes in meiosis


what is meant by product rule?

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


what is meant by sum rule?

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


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


what is meant by complementation?

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


why does linkage happen?

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


what indicates linkage?

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


how is RF calculated?

total recombinants/total progeny x100


what causes RF to reach 50%?

one or more chiasmata between 2 genes in every meiosis


what does a dominance test test?

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


what does a complementation test study?

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


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


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


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


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