Mendelian Genetics

Question 1

What is step 1 of Mendel’s Pea Plant Experiments?

Answer 1

Grew true breeding plants and called this the P generation (parent)

-Had true bred purple and white flowering plants

Question 2

What is step 2 of Mendel’s Pea Plant Experiments?

Answer 2

Set up monohybrid crosses:

• True bred plant with purple flower crossed with true bred plants with white flowers
• Produced an F1 Generation which all had purple flowers

-Showed that purple was the dominant factor and white was the recessive factor

Question 3

What is step 3 of Mendel’s Pea Plant Experiments?

Answer 3

F1 generation self fertilised

• White flowering plants reappeared in F2 generation
• 705 plants with purple flowers and 224 with white flowers
• Approximately 3:1 ratio

Question 4

What did mendel conclude?

Answer 4

• An organism inherits 2 factors (known as alleles) for a characteristic:
• Heriditary particles (Genes)
• Alternative Forms (Alleles)

-When the plant reproduces these 2 characteristics separate (segregate during gamete formation and end up in different gametes)

Question 5

What is Mendel’s law of segregation?

Answer 5

• Each gamete gives one factor (allele)
• Each offspring gets one factor from each parent
• Random fusion during fertilisation

Question 6

What is the rule of dominance?

Answer 6

• homozygous dominant factors express dominant response
• Heterozygous factors express dominant response
• Homozygous recessive factors express recessive response

Question 7

What are the ratios in mendels plant experiment?

Answer 7

3: 1 ratio of phenotypes
1: 2:1 ratio of genotypes

Question 8

What are alleles?

Answer 8

Different versions of the same gene

-Occurs due to variance in the sequence of nucleotide bases at the specific locus of the gene

Question 9

What is mendels law of independent assortment?

Answer 9

Genes get shuffled - these many combinations are one of the advantages of sexual reproduction

Question 10

What are dihybrid crosses?

Answer 10

cross between two different lines/genes that differ in two observed traits. In this case crossing yellow round peas with green wrinkled peas

Question 11

What is the ratio created in dihybrid cross?

Answer 11

9:3:3:1

Question 12

What are some recessively inherited disorders?

Answer 12

Cystic fibrosis, Tay Sachs disease, Sickle Cell Anaemia

-People can be carriers if only containing one recessive allele

Question 13

What are some dominantly inherited disorders?

Answer 13

Huntington’s disease, Achondroplasia (dwarfism)

Question 14

How does Huntington’s disease continue through generations?

Answer 14

Disease has no obvious effect until 35-45years old, usually after reproduction has occurred causing allele to be passed on to the next generation

Question 15

How many chromosomes does a diploid cell have?

Answer 15

2n = 46chromosomes (2sets)

Question 16

How many chromosomes does a haploid cell have?

Answer 16

n = 23chromosomes (1 set)

Question 17

What is mitosis?

Answer 17

Process by which cells are replicated for growth, repair

Question 18

What is meiosis?

Answer 18

Process by which gametes are produced

-produces 4 daughter cells, each haploid containing a single set of chromosomes

Question 19

What happens in meiosis?

Answer 19

Meiosis I:
-reductional division: homologous pairs are separated reducing the number of chromosomes by half

IPMAT

Meiosis II:
-equational division: -sister chromatids are seperated producing 4 haploid gametes (analogous to mitosis)

Question 20

How does independent assortment of chromosomes have an effect during meiosis?

Answer 20

• Leads to an individual producing a collection of gametes that differ greatly in the combinations of the chromosomes inherited from parents
• 2^23 is the number of possible combinations of maternal and paternal chromosomes (8.4million)
• Each chromosome is not entirely maternal or paternal origin because of the process of crossing over

Question 21

What is crossing over?

Answer 21

The DNA of 2 non-sister chromatids are joined and pieces of each chromatid are exchanged beyond the cross over point

• Produces recombinant chromosomes
• Average of 1-3 crossing over events per chromosome pair
• Occurs in Prophase I

Question 22

What is random fertilisation?

Answer 22

Any two gametes can come together to fertilise.

• in humans there are 70trillion diploid combinations
• adds to genetic variation

Question 23

What are the complications with Mendel’s laws?

Answer 23

Genotypic ratios follow Mendel’s laws but phenotypes do not

Question 24

What is incomplete dominance?

Answer 24

One trait is not really dominant over the other
-The phenotype of the heterozygous is intermediate between the phenotype of dominant and recessive traits - blending of the traits

Question 25

What is codominance?

Answer 25

When both alleles for a trait are expressed in heterozygous offspring
-the two dominant genes are expressed at the same time
Eg. ABO blood groups

Question 26

How are blood groups determined?

Answer 26

3 alleles for a single gene:
I(a) - Dominant for A group
I(b)- Dominant for B group
i - Recessive for O group

4 Phenoypes: A, B, AB, O

• I(a) and I(b) are co-dominant so both carbohydrates are present when they exist together in a genotype
• I(a) and I(b) are dominant over the i allele

Question 27

What is Pleiotropy?

Answer 27

Most genes have multiple phenotypic effect (pleiotropy)

Question 28

What is epistasis?

Answer 28

Phenotypic expression of a gene at one locus affects another gene at a different locus eg, labrador coat colour

-Second gene determines pigment production, if there is no dominant pigment allele then the dog will be yellow irrespective of the other alleles

Question 29

What is polygenetic inheritance?

Answer 29

• One character is influenced by many genes

- Eg, height, skin colour

Question 30

What instances occur where Mendel’s laws do not apply?

Answer 30

• Mitochondrial Inheritance -mtDNA is solely inherited through the maternal line
• LInkage - two genes that are close together physically
• Linkage disequilibrium - two alleles that are not inherited seperately