Lec 25

Question 1

What’s the importance of a test cross ?

Answer 1

a method used to know the genotype of the dominant phenotype .
It’s used to identify F2 tall plants as pure or hybrid
( hybrid لأنهم اهمه اللي ممكن يكونون )

Question 2

How do we preform a test cross ?

Answer 2

By crossing a test plant with a dwarf / recessive phenotype plant , and the offspring phenotypes will determine / predict the genotype of it

Question 3

What are the types of crosses ?

Answer 3

1- monohybird test cross ( أقارن نبتتين بصفة وحدة )
2- dihybird test cross ( أقارن بين نبتتين بصفتين مختلفتين )

Question 4

What’s a Heterozygous test plant ?

Answer 4

A plant that will produce 50% offspring with dominant hybrid phenotype & 50% with recessive phenotype
Hetero -> different so it is Tt

Question 5

What’s a Homozygous test plant ?

Answer 5

A plant that will produce 100% offspring with a Dominant recessive phenotype only
Homo -> same so it’s TT

Question 6

What are factors ?

Answer 6

Genes / alleles that are located on the chromosome

Question 7

Humans have—— pairs of chromosomes

Answer 7

23
22 pairs autosomes
1 pair sex chromosomes

Question 8

A functional part of the chromosome/DNA that encodes RNA/protein/phenotype

Answer 8

Gene

Question 9

The active part of genome is ?

Answer 9

Euchromatine
§ all genes contain <2% of these functional genes

Question 10

What’s locus ?

Answer 10

Location of a gene on a chromosome

Question 11

What’re transposons/mobile genes?

Answer 11

Genes that can change / move from their locus

Question 12

Gene locus is usually——, but some genes are not .

Answer 12

Fixed

Question 13

Non functional genes

Answer 13

Heterochromatin
§ all genes contain 98% of these nonfunctional genes

Question 14

What’s genetransposition ?

Answer 14

It’s the rarest phenomenon in which the gene moves , which causes abrupt changes in phenotypes ( تسبب أمراض )

Question 15

Allele

Answer 15

An alternative form/variant/additional copy of a gene

Question 16

Both copies of a gene at a locus make an ——

Answer 16

Allele pair

Question 17

Homozygous

Answer 17

Alleles on locus are same

Question 18

Heterozygous

Answer 18

Alleles on locus are different ( hybrid/carrier )

Question 19

Hemizygous

Answer 19

Only very small amount of DNA is same in these chromosomes

Question 20

Signs/symptoms/features that can be seen , detected , measured

Answer 20

Phenotypes

Question 21

A ——— predicts the phenotype of a gene

Answer 21

Genotype

Question 22

An autosomal recessive disease caused by a gene on chromosome 12

Answer 22

Phenylketonuria

Question 23

A cross between 2 plants with 2 traits each with pure contrasting phenotypes

Answer 23

Dihybird cross

Question 24

Dihybird cross supports the law of dominance , explain ?

Answer 24

In dihybird cross only one factor of each trait is expressed, and the second factor didn’t get expressed.

Question 25

Yellow Round ( YYRR ) x green wrinkled ( yyrr ) What are the offsprings ?

Answer 25

YyRr Yellow round dihybrids 100%

Question 26

Self crossing of F1 dihybirds YyRr x YyRr

Answer 26

نفصلهم إلى : YR , Yr , yR , yr [ 4 types of gamete are produced ] -> law of segregation نسوي جدول بانت بأرع خانات فوق و جنب Offspring: YYRR , YyRR , yyRr , yyRR , yyrr Yellow Round = 9/16 Yellow wrinkled = 3/16 green Round = 3/16 green wrinkled = 1/16 Phenotype ratio -> 9:3:3:1

Question 27

What’s the result of self crossing the F1 dihybirds ?

Answer 27

The recessive phenotypes reappeared by law of segregation & dominance + low of independent assortment

Question 28

Low of assortment suggest that

Answer 28

Genes don’t interact, they assort randomly during fertilisation

Question 29

Interpretation of F2 dihybird findings:

Answer 29

-Each trait maintains its monogenic ratios -Genes don’t interact with each other so they assort randomly without influencing each other ( law of independent assortment ) -only 1/9 were pure Yellow Round

Question 30

We’re dihybird test crossing between : yyrr ( recessive ) x test plant Offspring : yyRr What’s the test plant genotype ?

Answer 30

1- gametes: yr from recessive | remove it from the offspring ( green Yellow ) 2- -> we will have yR from offspring so gametes are yR The test plan is yyRR

Question 31

We’re dihybird test crossing between : yyrr ( recessive ) x test plant Offspring: YyRr ( Yellow Round ) & Yyrr ( Yellow wrinkled ) What’s the test plant genotype ?

Answer 31

1- Gametes : yr from recessive | remove it from bothoffsprings 2- -> we will have YR & Yr so gametes are YR & Yr The test plant is YYRr

Question 32

What’re the test plant gametes genotypes when dihybird test crossing of the following: 1- YYRR 2- Yyrr 3- YyRr 4- yyrr

Answer 32

Gametes: 1- YR 2- Yr & yr 3- YR & Yr & yR & yr 4- yr

Question 33

Medical relevance:

Answer 33

1. Predict disease inheritance 2. Genetic counselling 3. Preventative Measures

Question 34

What’re types of human diseases based on ( number, locus ,inheritance of gene ) :

Answer 34

1- monogenic ( single gene defect ) £ autosomal diseases { gene on autosome } £ sex / X-linked diseases { gene on sex chromosome } The phenotypic ratio will be different 2- multigenic ( multi gene defect )