Genetics Leah Flashcards

Describe a diploid nucleus

Has chromosomes organised into homologous pairs

What are the only cells in the human body that are haploid?

Gametes/sex cells

What is a zygote?

A diploid cell formed when two haploid nuclei fuse together, matching up their chromosome pairs

What are the conditions for a monohybrid cross

Parents are both homozygous for opposite traits, and the experiment only focuses on one trait

What is the expected ratio for the F1 generation in a monohybrid cross

1 for both phenotype and genotype (all offspring have the same)

What is the expected ratio for the F2 generation in a monohybrid cross

Genotype 1:2:1, phenotype 3:1

What is one pro and con to self-pollination

• used by farmers for practical agriculture

• less genetic diversity makes species vulnerable to environment adaptations

Phenotype refers to observable traits, why might observable be a problematic word choice?

Not all phenotypic traits are visible, such as blood type

What is phenotypic plasticity?

An organism's ability to express its phenotype differently depending on the environment

Provide one example of phenotypic plasticity for physiology

Birds activate genes to produce more digestive maltase enzymes when more grain is available than insects

Provide one example of phenotypic plasticity for morphology

Plants can activate genes that produce growth hormones to make thicker leaves when it senses there is more light available

Provide one example of phenotypic plasticity for behaviour

Animals can modify their foraging behaviour depending on the types of foods available in their environment from one season to the next

What is it mean for a disease to be autosomal?

No linked to sex chromosomes

Provide 3 examples of an autosomal recessive disease

Cystic fibrosis, sickle cell disease, albinism

What does SNP stand for and what does it mean?

single-nucleotide polymorphism = occur when a nucleotide of the genetic code is not found where it is expected and another is found in its place

Explain incomplete dominance

One allele is not completely dominant over the other, no recessive alleles, a heterozygous incomplete dominant genotype expresses a new trait

Explain co-dominance

Both alleles for a trait are expressed simultaneously in a heterozygote (AB blood type)

What is polygenetic inheritance?

Involves two or more genes influencing the expression of a trait

What is meant by continuous variation?

There are multiple alleles and therefore an array of phenotypes can be produced

What is special about the telomere at the end of chromosomes?

It is a region of repetitive DNA sequences at the end of a chromosome, they protect the end of chromosomes from becoming frayed or tangled

What happens to the telomeres each time the cell divides?

They become shorter

Explain the chromosome 2 hypothesis

Two chromosomes from an earlier common ancestor fused together, explaining why modern humans have 46 chromosomes while other primates have 48

What is satellite DNA?

Short repeating sequences non-coding of DNA found in the centromere and telomere regions

Why is mitochondrial only passed from mother to offspring?

Sperm's mitochondrial DNA never enters the egg, and therefore the DNA isn't shuffled as with chromosomal DNA

What is mitochondrial DNA used for?

Comparing organisms within a species or those who have diverged recently, used to determine haplogroups (ethnic groups with different mDNA) and traces movement of people around the world

What are other methods for comparing how similar/different species are from one another?

Comparing amino acid sequences, phylogenetics

Why is genomic testing useful?

Having a detailed ancestry report and help to discover DNA related health issues, and possibly personalised medicine can be made based on the sequencing of genomes

Why have some countries made this illegal?

Laws have been put in place to protect people's privacy e.g. a parent who has put their child up for adoption who does not want to be identified

What 3 components does every nucleotide include

5-carbon deoxyribose, phosphate group, nitrogenous base

Why is the replication process of DNA said to be semi-conservative?

According to the semiconservative model, after one round of replication, every new DNA double helix would be a hybrid that consisted of one strand of old DNA bound to one strand of newly synthesised DNA

What are the enzymes needed for replication?

Primase, ligase and a group of enzymes collectively called DNA polymerase

What is the first stage of DNA replication? Describe

The separation of the double helix into two single strands by helicase - the helicase unwinds the DNA at the origin of replication moving in both directions

What happens once the DNA is unzipped?

• The hydrogen bonds are broken and bases are unpaired, and instead they form complementary pairs with the free-floating nucleotides available

• DNA polymerase enables this

What does PCR stand for?

Polymerase chain reaction

What are the components needed to run a PCR

Primers, taq polymerase, free nucleotides

Why is taq polymerase used?

It's a polymerase from a bacterium that lives in hot spring and can therefore withstand high temperatures

Describe step 1 of PCR

Denaturation: the mixture is heated between 92ºC and 98ºC, breaking the hydrogen bonds between DNA strands

Describe step 2 of PCR

Annealing: the mixture is cooled between 50ºC and 65ºC to allow the primers to bind with nucleotides on both strands

Describe step 3 of PCR

Elongation: The Taq polymerase catalyses the building of new DNA strands by extended the primers. A temp of 70-80ºC is needed for this steps

What is gel electrophoresis used for

separate DNA fragments by size to justify its origin

Describe the process of gel electrophoresis

Restrictive enzymes are used to chop up the long filaments of DNA into varying sizes of fragments If two different sources of DNA are compared the same enzymes are used to produce fragments

The DNA fragments are placed in small wells in a gel placed in an electrophoresis chamber

The gel is exposed to an electric current, positive on one side, negative on the other

DNA has a negative charge due to the phosphate, therefore it moves towards the positive end

The biggest, heaviest and least charged particles do not move easily through the gel. The smallest, least massive and most charged particles pass through the gel more easily

At the end, fragments leave a banded pattern of DNA

What is DNA profiling/DNA fingerprinting

The process of matching an unknown sample of DNA to a known sample

Define genes

The sections of DNA that code for proteins

What is the difference between transcription and DNA replication?

Only one strand is used as a template strand to create messenger RNA

When does transcription begin?

RNA polymerase binds to a promoter sequence near the beginning of a gene on the template strand

Which DNA strand serves as the template for mRNA synthesis?

The antisense (non-coding) strand

Which strand has the same sequence as the RNA (except U replaces T)?

The sense (coding) strand

What bonds hold the DNA strands together and must be broken during transcription?

Hydrogen bonds

What two main functions does RNA polymerase perform during transcription?

1) Unzips DNA by breaking hydrogen bonds (helicase-like), (2) links RNA nucleotides together.

Can DNA be reused as a transcription template?

Yes, because DNA is stable and unchanged by transcription.

What is the consequence of a mutation in DNA on transcription?

It may change the mRNA sequence and the resulting protein.

Do all genes transcribe simultaneously?

No, genes are expressed at different times depending on cell needs and development.

What role does transcription play in gene expression?

It turns genes on or off by controlling RNA production.

What does one mRNA molecule typically code for?

One polypeptide

What is translation?

The process where ribosomes read mRNA and assemble amino acids into polypeptides.

What are the three main types of RNA and their functions?

mRNA → carries genetic code to ribosome

tRNA → brings amino acids to ribosome

rRNA → forms ribosomes with proteins

What is a codon?

A sequence of three RNA bases coding for one amino acid

What is an anticodon?

A sequence on tRNA complementary to an mRNA codon

What is the start codon and which amino acid does it code for?

AUG → Methionine.

Name the three stop codons.

UAA, UAG, UGA.

Why is the genetic code called "degenerate"?

Multiple codons can code for the same amino acid.

Why is the genetic code "universal"?

It is shared by almost all organisms.

What is a mutation?

A random permanent change in DNA sequence.

Name the three types of gene mutations.

Substitution, insertion, deletion.

What is a point mutation?

A mutation involving a single nucleotide.

What causes a frameshift?

Insertions or deletions not in multiples of three.

Give an example of a disease caused by substitution mutation.

Sickle-cell disease (GAG → GTG).

Give an example of a disease caused by insertion mutation.

Huntington's disease (CAG repeat expansion).

Give an example of a disease linked to a deletion mutation.

HIV resistance (CCR5 delta-32 mutation).

What are mutagens?

Agents that increase mutation rates (e.g., radiation, chemicals, free radicals).

Which enzyme proofreads and corrects DNA replication errors?

DNA polymerase

What is the difference between germ cell and somatic cell mutations?

Germ cell mutations are inherited, somatic mutations are not.

What is a mutation hotspot?

A DNA region prone to mutations, such as CpG sites.

What is an allele in relation to mutation?

A new version of a gene created by mutation.