Monohybrid crosses, test crosses and back crosses Flashcards Preview

BLGY1232 Introduction to genetics > Monohybrid crosses, test crosses and back crosses > Flashcards

Flashcards in Monohybrid crosses, test crosses and back crosses Deck (17):
1

Give 5 rules for nomenclature of genes.

1. Gene names are always written in italics
2. Dominant alleles are always written first
3. Dominant alleles are written in capitals
4. Recessive alleles are written in lower case
5. Wildtype alleles are often denoted by '+'

2

What are the two effects of the yellow gene in mice which makes it pleiotropic?

Lethality and coat colour

3

What happens if the mouse is homozygous for the yellow gene?

The zygote would not survive so they are not found

4

How are loci often represented?

Three letters that are an abbreviation of the gene name

5

What ratio would be produced by a cross between two F1 heterozygotes?

3:1

6

What other method can be used to represent crosses that isn't a punnet square?

Branch diagrams

7

Why are branch diagrams useful?

They represent the outcome of crosses when there are multiple genes involved better than a punnet square can.

8

How would Ss be represented in its gametes in a branch diagram?

1/2S , 1/2s

9

What is a test cross between?

A plant with the dominant phenotype and a homozygous recessive plant

10

what would be the result of a test cross if the dominant parent plant was homozygous?

All of the progeny would show the dominant phenotype

11

What would be the result of a test cross if the dominant parent was heterozygous?

There would be a 1:1 ratio of dominant phenotype to recessive phenotype.

12

What are the two ways of determining the genotype of a dominant phenotype?

1. Self the F2 plants
2. Do a test cross

13

What is a back cross?

A cross between an individual and one of its parents

14

What is intermediate dominance?

Neither of the parental traits are dominant over the other

15

What is the result of intermediate dominance?

Blending of dominant traits

16

What would a back cross of yellow progeny to wild type show?

All yellow mice are heterozygous

17

What is the problem with doing a back cross of yellow progeny to wild type?

YY is lethal so a class of progeny is missing from the 3:1 ratio.