3.2. Genetics 2

Question 1

Different types of mutations based on how/if they affect the gene/polypeptide chain

Answer 1

same-sense don’t change the amino acid that the gene codes for, non-sense mutations code for a stop codon instead of an amino acid, and mid-sense mutations result in a codon that codes for a different amino acid.

Question 2

Which number of nucleotides should be deleted or inserted to cause least “damage” to the gene/polypeptide chain?

Answer 2

three because only one is added or removed but the rest of the polypeptide chain stays the same – if the number of nucleotides inserted/deleted is not three or three’s multiple, then the entire reading frame is changed (all a-a different) and this is called a frameshift mutation.

Question 3

Sickle-cell anemia

Answer 3

an example of substitution mutation which results in a deficiency of properly functioning erythrocytes - different allelic forms of Hb: Hb^n (normal adult) and Hb^f (fetuses). If Hb^n mutates Hb^s is formed which codes for abnormal Hb. Codon GTG -> GAG (valine -> glutamic acid). The different chemical properties of the two a-a (valine is hydrophobic, glutamic acid is negatively charged) cause different secondary and tertiary structures of Hb which changes its overall conformation and therefore function. The new Hb can carry much less O2 than normal. Sickle cells are also deformed so they can stick together and form clumps which impairs the blood flow and can even lead to a stroke.

Question 4

Explain the connection between malaria and sickle cell allele

Answer 4

Hb^n Hb^n genotype is healthy but, if infected, suffers badly from malaria, Hb^s Hb^s cannot be infected by malaria as plasmodium can only survive in healthy erythrocytes but it suffers badly from anemia, and the Hb^s Hb^n genotype suffers mild anemia and is protected from malaria (plasmodium cannot survive in their blood due to some chemical imbalances.

Question 5

Germ vs somatic cells

Answer 5

Germ cells are cells produced in meiosis (sex cells). Somatic cells are body cells.

Question 6

Give two examples of a positive gene mutation

Answer 6

1) the development of lighter skin (less melanin needed to protect the skin from light) in places with less sun enables greater absorption of UV light which turns previtamin D into vitamin D
2) lactase production in adults (should be limited only to babies) – they increase a population’s genetic variability.

Question 7

Gene knockout

Answer 7

the latest technique to study the function of unknown genes – organisms with dysfunctional variations of a gene of interest are made and the change in the phenotype (and behavior of the organism) reveals the gene’s function – e.g. p53 (higher tumor incidence and age faster).

Question 8

CRISPR

Answer 8

Cluster Regularly Interspaced Palindromic Repeats is a new gene editing technology based on the immune system naturally present in prokaryotes that helps them evade viral infection – they remember (molecular memory) an old phage infection by taking a part of its DNA (spacer) each time – different spacers are separated by repeats and once a virus infects the organism a specific spacer and its repeat get transcribed to form gRNA (guide RNA) which cuts the viral DNA in order to deactivate it – CRISPR enables us to insert/delete sections of the DNA into cells with extreme precision (consists of Cas 9 protein (that detects viral DNA and destroys it) + CRISPER region of prokaryotic DNA).

Question 9

Particulate inheritance

Answer 9

traits are determined by genes/alleles that separate during meiosis and reunite upon fertilization – the genes don’t lose their integrity but may be overshadowed by the intensity of another gene (dominant and recessive genes).

Question 10

What is used to trace the transmission of hereditary traits

Answer 10

hybridization (controlled pollination)

Question 11

Seven alternative phenotypic traits of edible peas

Answer 11

flower color/position, seed color/shape, pod color/shape, and height

Question 12

Phenotype vs genotype

Answer 12

phenotype is the set of all expressed traits (characteristics) determined by the genotype and genotype is all alleles possessed by an organism (genetic potential)

Question 13

Monogenic vs polygenic trait

Answer 13

polygenic is determined by multiple genes, and monogenic by a singular gene

Question 14

Homozygous vs heterozygous genome

Answer 14

homozygous either DD or RR (no hidden, recessive alleles, purebred – heterozygous has two different alleles, D and R

Question 15

Filial generation and Punnett square

Answer 15

filial is the first generation whose genotype and phenotype we’re following in a crossing. We look at their offspring’s genotypic and phenotypic ratios using a Punnett square (grid).

Question 16

Monohybrid vs dihybrid cross (compare ratios)

Answer 16

monohybrid is the cross-fertilization to see how a single trait gets inherited (genotypic ratio 3:1) – dihybrid is the cross in which parents differ in two traits that are controlled by two different, non-linked (in most cases) genes – the phenotypic ratio for F2 is 9:3:3:1 (from purebred parental generation) – just not the case when two genes interact, then the ratio changes (albino and color example)

Question 17

Two laws of genetics

Answer 17

1) Law of segregation of alleles – two alleles separate into different haploid daughter nuclei during meiosis and then reunite in fertilization
2) the law of independent assortment – the presence of an allele of one of the genes in gametes has no influence over which allele the other gene is present in that gamete (two bivalents orient independently during division which results in the potential creation of four different gametes)

Question 18

Explain different possible relations between different gene alleles

Answer 18

1) dominant: an allele that has the same effect on the phenotype in both homozygous and heterozygous states –
2) recessive: an allele influences the phenotype only when in the homozygous state
3) co-dominant alleles: a pair of alleles that both influence the phenotype when in a heterozygous state (third phenotype where both are completely expressed, e.g. erythrocyte blood groups)
4) incomplete dominance: alleles combine so the result is a third, intermediate (blending) phenotype

Question 19

Carrier

Answer 19

an individual that has a recessive allele of a gene that has no effect on its phenotype (heterozygous) – the allele gets passed on to the next generation but is not expressed in this individual

Question 20

Test cross

Answer 20

crossing done between any genotype and a homologous recessive one when we’re interested in a genotype of an individual that displays a dominant phenotype. Test crosses always result in a 1:1:1:1 phenotypic ratio

Question 21

Alternative vs multiple allelic forms (examples)

Answer 21

alternative Rhesus factor (+ or -), that is gene D – erythrocyte blood group (RBC) which codes for different antigens (AG) on the cell surface: AG A and AG B (I^A,I^B alleles). I^A, I^B and i encode different types of glycoproteins embedded in the RBC membrane

Question 22

Pedigree chart

Answer 22

a diagram that shows the occurrence and appearance of phenotypes of a particular gene of an organism and its ancestors from one generation to the next