Dominant/Recessive

Question 1

who was Gregor Mendel

Answer 1

• An Austrian monk with a love of gardening.
• He noticed that certain characteristics appeared in only 2 forms with no blending of the traits.
• He cross-pollinated thousands of pea-plants and discovered that the ratios in which the traits appeared in the next generation was predictable.
• His findings are now held in such high regard that the field of inheritence is called MENDELIAN GENETICS.

Question 2

what are alleles

Answer 2

many genes have 2 or more forms called alleles.

Question 3

what two forms can alleles be in

Answer 3

homozygous
heterozygous

Question 4

homozygous

Answer 4

Homozygous
(also called true-breeding or pure-bred)
having 2 copies of the same allele
- inheriting the same allele from each parent.

Question 5

heterozygous

Answer 5

Heterozygous (also called hybrid)
having 2 different alleles
- inheriting a different allele from each parent

Question 6

how do we know if the inheritance is dominant/recessive? plus eg’s

Answer 6

When only 2 forms of the gene are shown, the form of inheritance is known as dominant/recessive inheritance.

eg dimples/no dimples, free lobe/attached lobe

Question 7

dominant

Answer 7

The trait that is shown is known as dominant and the allele that is responsible for this trait is given a capital letter as its symbol.

Question 8

recessive

Answer 8

The trait that is not shown is known as recessive and the allele that is responsible for this trait is given a lower case letter as its symbol

Question 9

what makes a heterozygote different to a homozygote

Answer 9

the heterozygote has the alleles for both forms of the trait [eg the DNA to make dimples and no dimples]
but only one of the forms is expressed or shown.

Question 10

show the different symbols with earlobes

Answer 10

B - free ear lobe
b - attached ear lobe

BB - homozygous dominant
Bb - heterozygous dominant
bb - homozygous recessive

Question 11

genotype

Answer 11

The genetic makeup of an organism is called its genotype eg BB, Bb, bb

Question 12

phenotype

Answer 12

The way in which the trait is expressed is called the phenotype eg dimples, curly hair.

Question 13

what can affect the phenotype + eg

Answer 13

The phenotype is a combination of the genotype and the environment.

Identical twins have the same genotype but they may have a different phenotype if they live in different areas or have a different lifestyle.

Question 14

good letters to use as symbols

Answer 14

Aa Bb Dd Gg Ee Hh Tt

Question 15

how do we predict genotypes and phenotypes?

Answer 15

using Punnett squares

Question 16

steps to creating/using a Punnett square

Answer 16

1. assign genetic symbols eg F/f
2. construct Punnett square with genotype of parent one on the top and genotype of parent two on the side
3. using the Punnett square write in any possible combinations as the genotype including percentages (should add to 100%)
4. using the genotypes work out what the possible outcomes of the phenotype could be and the percentage of each outcome occurring

Question 17

why does the Punnett square reset?

Answer 17

The punnett square “resets” after each offspring is born because the genotypes/alleles don’t change.

i.e. the genotype of the 1st child of a couple has NO effect on
the possible genotypes of any future offspring as that child will involve a new sperm and a new egg.

Question 18

F1 vs F2 generation

Answer 18

F1 generation - the offspring of two parents
F2 generation - the result of the interbreeding of the F1 gen

Question 19

when would you be asked to interbreed the F1 gen

Answer 19

You will only ever be asked to do this if the original parents are both
homozygotes meaning that all of the F1 gen have the same genotype.