524- Genetics

Question 1

What is DNA?

Where is it found?

Answer 1

> genetic instructions for how a body is formed and how it functions

> in the nuclei of our cells

Question 2

What is a chromosome?

Answer 2

Organised length of DNA

Question 3

What are homologous chromosomes?

Answer 3

they are pairs of chromosomes (1 from each parent) that are similar in size and carry info about the same traits (different alleles).

Question 4

What is a gene?

how many do we have?

Answer 4

section of DNA in a SPECIFIC location on a chromosome that has info that determines a trait.
We have 2 copies of a gene (1 from each parent) that have 2 alleles each

Mom Dad
1 gene = 1 gene
2 alleles 2 alleles

Question 5

What is an allele? (location, how’s it formed)

Answer 5

an alternative form of a gene– they are paired genes in the same position on homologous chromosomes

> slight differences in the base sequence cause variations in phenotypes, which leads to genetic variation between people

ex) wet earwax, dry earwax

Question 6

Where do our genes come from?

Answer 6

2 sets of chromosomes one from each parent!

Question 7

What is the name for the sides of a double chromosome (homologous chromosome)?

Why do they need to have identical genetic info?

Answer 7

> (sister) chromatid

> it needs to have identical info from each other so that when it splits during cell division, each new cell will have the same genetic info!

Question 8

What is the difference between somatic cells and gametes?

Answer 8

> somatic cells: are any cells in the body which is not a sperm or an egg- they are diploid

> gametes: sex cells (sperm and egg)- they are haploid.

Question 9

Difference between haploid and diploid.

Answer 9

haploid: 1 set of chromosome
(23 chromosome-gametes)

diploid: 2 sets of chromosomes, one from each parent (23 pairs).
(46 chromosomes- somatic cells)

Question 10

Why do gametes only have 23 chromosomes (haploid)?

Answer 10

so that when fertilisation occurs, the no. is restored to 46 (diploid).

Question 11

Difference between sex chromosomes and autosomes?

Answer 11

> Sex chromosomes: only 1 pair (last one) which determines the person’s genetic sex. XX (female), XY (male)

> Autosomes: the other 22 pairs of chromosomes which help determine most traits.

Question 12

What is a karyotype? (describe)

Answer 12

display of all chromosomes from 1 diploid cell, from longest to shortest. Shows 22 autosomes and last pair are sex chromosomes

Question 13

Difference between mitosis and meiosis

location, division, daughter cells…

Answer 13

⭐mitosis: (in all body organs)
one cell division, making 2 identical daughter cells (46 chromosomes/diploid= somatic cells)

⭐meiosis: (only in gonads)
2 cell divisions, makes 4 daughter cells (23 chromosomes/haploid=gametes)

Question 14

Explain difference of dominant and recessive alleles

Answer 14

⭐ Dominant alleles is where 1 allele masks another’s expression (W)- always expressed if present (STRONGER version of gene)

⭐ Recessive alleles - weaker version of gene- only expressed when 2 are present

Question 15

Difference between heterozygous and homozygous alleles?

Answer 15

⭐heterozygous: got 2 different versions of an allele from each parent (1 dominant, 1 recessive=Ww)

⭐homozygous: 2 of the same allele, 1 from each parent (ww/ WW)

     >ww: homozygous recessive
     >WW: homozygous dominant

Question 16

Difference between genotype and phenotype?

Answer 16

⭐genotype: genetic makeup of person
-we have 2 copies of each gene, 1 from each parent and each gene has 2 alleles

ex) WW

⭐phenotype: physical expression of the genotype (alleles) (what you can see)

ex) wet earwax

Question 17

What are punnet squares?

Answer 17

They show the interaction between dominant and recessive alleles, and predict possible gene combos for kids if parents genotypes are known.

ONLY shows A PROBABILITY of a genotype, therefore phenotype.

Question 18

What are the 3 principles of inheritance?

briefly explain

Answer 18

⭐ Independent assortment
>during meiosis- gene pairs (1 from mom and 1 from dad) are split into gametes.

⭐ Crossing over of homologous chromosomes
> tips of homologous chromosomes trade genetic info

⭐ Random fertilisation
> during fertilisation, gene pairs are randomly reunited making a new genotype!
Interaction of alleles determines phenotype

Question 19

What are the 4 types of inheritance?

Answer 19

1) Single gene inheritance
2) Sex-linked inheritance
3) Multiple- allele inheritance
4) Polygene inheritance

Question 20

What are the characteristics of single gene inheritance?

Answer 20

⭐condition or trait is either present or absent

• 1 gene controls specific trait. There are only 2 possible alleles for each gene
  ex) wet earwax, dry earwax

Question 21

Are (most) genetic disorders inherited as dominant or recessive alleles? (example)

Answer 21

recessive

• albinism, cystic fibrosis

Question 22

What is a carrier?

Answer 22

heterozygous for recessive condition.
their phenotypes are normal due to the presence of a dominant allele, however, they can pass on the recessive allele to their offspring.

Question 23

1) What are autosomal conditions?

2) What are the 2 types?

Answer 23

1) genetic conditions carried on 1 of the 22 autosomes, both sexes can have them (because they’re in the autosomes)

2)
⭐Autosomal Dominant
-1 copy of dominant allele (heterozygous)
: homozygous dominant- 2 copies of disorder causing allele (potentially LETHAL)
ex) huntington’s disease

⭐Autosomal Recessive

• only when 2 copies of recessive allele is present
  ex) cystic fibrosis

Question 24

What is sex-linked inheritance?

Answer 24

⭐traits/ conditions determined by genes in (usually the X)
the sex chromosomes are passed on to offspring.

-they are more common in males, (females mostly will be carriers unless both X chromosomes carry that gene)

ex) balding (gene in X chromosome)-
rare to see in women because they have both XX but shows more in men because they have XY, if they have the balding gene trait from mom, the Y cannot counter/mask against this.

ex) haemophilia, red-green colour-blindness

Question 25

What is Multiple-allele inheritance?

Answer 25

⭐a gene has 2 or more alleles

Ex) ABO blood groups

3 possible alleles, but each person can only have 2 (one from each parent)
O is recessive to both A & B!

Question 26

What is polygene inheritance?

Answer 26

⭐ there are 2 or more pairs of genes (in different chromosomes) that influence this trait.

> the result is a trait that has continuous variations in phenotype

Ex) skin color, height, eye color, basal metabolic rate

• most traits are determined by this!