SAC 4 (Inheritance)

Question 1

human somatic body cells

Answer 1

• 46 total chromosomes
• 44 autosomes (non sex chromosomes)
• 2 sex chromosomes (XX or XY)

Question 2

size and number of autosomes

Answer 2

• numbered chromosome pair 1 the largest and chromosome pair 22 the smallest
• telomere is located at the end of each chromosome
• p-arm is the short arm
• q-arm is the long arm

Question 3

genes

Answer 3

• section of DNA with particular sequence
• used to make proteins (which create the phenotype)
• are found in specific locations within a chromosome

Question 4

allele

Answer 4

• version of the gene

Question 5

genotype

Answer 5

• combination of alleles for a gene
  e.g (BB, Bb or bb)

Question 6

phenotype

Answer 6

• physical characteristic
  e.g (free or attached earlobes)

Question 7

squares and crosses

Answer 7

BE ABLE TO COMPLETE PUNNET SQUARES, MONO, DI AND TEST CROSSES

Question 8

dominant and recessive alleles

Answer 8

DOMINANT - always shown in the phenotype and masks recessive
- homozygous dominant (BB) (free earlobes)
- heterozygous (Bb) (free earlobes) (also carrier)
RECESSIVE - only shown if there are two recessive
- homozygous recessive (bb) (attached earlobes

Question 9

incomplete domiance

Answer 9

• when two alleles are equally dominant and ‘blend’ to form new phenotype
  e.g (red flower allele and white flower allele form pink petal flowers)

Question 10

codominance

Answer 10

• when two alleles are equally dominant and both are expressed in the phenotype
  e.g (red flower allele and white flower allele produce red and white petal flowers)

Question 11

meiosis v mitosis

Answer 11

• mitosis - 2 genetically identical (diploid 2n) (two copies of each chromosome) somatic cells
• meiosis - 4 genetically unique (haploid gametes n) (one copy of each chromosome) sperm and egg
• homologous chromosomes pair in prophase 1 of meiosis but not mitosis

Question 12

meiosis

Answer 12

• start with parent cell (paternal and maternal inherited chromosomes) (diploid cell)
• meiosis 1 (PMAT) - homologous chromosomes separate
• meiosis 2 (PMAT) - chromatids separate
• resulting in 4 haploid gametes

Question 13

crossing over - prophase 1 meiosis

Answer 13

• increases genetic variation by producing different allele combinations
• gene locus ‘G’ (location)
• chiasmata join and break to swap chromosome section
• where they join is random
• can be multiple
• goes through both meiosis 1 and 2 to produce gametes

Question 14

meiosis errors - non disjunction and incorrect separation

Answer 14

• if occurs in meiosis 1, none of the daughter cells will be correct and have usual haploid set of chromosomes (could result in trisomy’s)
• if occurs in meiosis 2, 2 daughter cells will be correct and 1 will have a chromosome missing and 1 will have an extra (could result in XO = turner syndrome - only have one sex chromosome)
• if any other chromosomes are missing it is not viable

Question 15

different trisomy’s

Answer 15

13 - patau syndrome
18 - edward syndrome
21 - down syndrome
XXY or XXXY - klienfleter syndrome

Question 16

independent assortment

Answer 16

• increases genetic variation through the random allocation of maternal and paternal chromosomes to gametes
• many combinations are possible due to 23 pairs

Question 17

sex linked traits

Answer 17

• if the gene locus is on the X chromosome the trait is said to be X-linked
• if the gene locus is on the Y chromosome the trait is said to be Y-linked
• males only have one X chromosome, the sex of a baby affects how likely it is to express a X trait
• only males have Y-linked traits
• allele symbols are written as with the X chromosome

Question 18

test crosses

Answer 18

• the unknown genotype individual is bred with a homozygous recessive genotype
• the homozygous recessive can only produce one type of genotype
• so the offspring phenotype will reveal the genotype of the unknown parent
  e.g (if black parent rabbit either BB or Bb is bred with white parent rabbit bb, if any offspring is white the black parent rabbit is Bb and if all offspring is black the black parent rabbit is BB)

Question 19

epigenetics

Answer 19

• the influence of environment of expression of genes
• protein polypeptide produce the phenotype
  e.g (protein tyrosinase produces melanin which is a pigment in skin, eyes and hair)

Question 20

epigenetic changes

Answer 20

• additions of methyl groups (CH3) to DNA are increased and decreased by environmental changes
• more methyl groups reduce gene expression
• are passed to offspring through heritable processes
  e.g (methyl groups added to cytosine which reduce ability to produce RNA and therefore less protein is produced)

Question 21

karyotypes

Answer 21

• number and appearance of chromosomes in the nucleus of a eukaryotic cells
• ordered by size from 1 - 22, then the sex chromosomes (XX or XY)

Question 22

polygenic inheritance

Answer 22

• phenotype controlled by more than two genes
• each gene contributes ‘a bit’ to produce variation
  e.g (height, eye and hair colour)