Genetics Flashcards
What are somatic cells?
Body cells that do not produce gametes
What are germ cells?
Diploid reproductive cells that give rise to gametes
What are diploid cells?
Cells with 2 sets of chromosomes
What are haploid cells?
Cells with 1 set of chromosomes
What are autosomes?
Chromosomes that do not determine sex
What is a karyotype?
An ordered display of the pairs of chromosomes in a cell
What are the 5 stages of mitosis?
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
When does mitosis occur in the cell cycle?
Before cytokinesis, and after G2 in the cell cycle
What are the two sets of cell division in meiosis?
Meiosis I and meiosis II
Out of meiosis I and II, which is the reductional division?
Meiosis I, as homologous chromosomes separate
What happens in meiosis II?
Sister chromatids separate
What 3 mechanisms in meiosis contribute to genetic variation?
- Independent assortment
- Crossing over
- Random fertilisation
When does independent assortment occur?
Metaphase I of meiosis
When does crossing over occur?
Prophase I of meiosis
What is random fertilisation?
During sexual reproduction, the male gamete and female gamete that fuse are selected randomly from the pool of male and female gametes
What are epigenetic influences?
Modifications of gene expression that occur without changes in the underlying DNA sequence
What is co-dominance of alleles?
Co-dominant alleles are alternative forms of a gene, in which if they are both present, they will both be expressed independently, and their effects will be combined in the phenotype of the individual
What does F1 refer to?
F1 refers to the first generation, which is the offspring of a cross between two pure-breeding individuals
What is the F1 generation often studied to reveal?
How traits are inherited from parent to offspring
What does F2 refer to?
F2 refers to the second generation, which is the offspring between two F1 individuals
What is the F2 generation often studied to reveal?
How traits are inherited from grandparents to grandchildren, and can help determine the mode of inheritance for a particular trait
What is a one-factor cross also known as?
Monohybrid cross
What is a one-factor cross?
A cross between individuals that differ in only one trait
What is the purpose of one-factor crosses?
The inheritance of a single trait is analysed, and the ratio of phenotypic and genotypic ratios in the offspring are used to determine mode of inheritance of the trait
What is Mendel’s first law also known as?
The law of segregation
What does Mendel’s first law state?
During gamete formation, the two alleles of a gene segregate from each other, with each gamete only receiving one of the two alleles
What is Mendel’s second law also known as?
The law of independent assortment
What does Mendel’s second law state?
Alleles of different genes are distributed randomly into gametes, and inheritance of one trait does not affect the inheritance of another
What are physically linked genetic loci?
When two genetic loci are located on the same piece of DNA, so their alleles tend to be inherited together
What process can alter the inheritance of physically linked loci?
Meiotic recombination/crossing over
What factor affects how likely physically linked loci are going to be inherited together and why?
The distance between the two loci on the chromosome affects how likely they are to be inherited together.
The closer they are, the less likely they are to be separated during crossing over, and so the more likely they are to be inherited together
What is a chromosomal aneuploid?
An abnormal number of chromosomes, either due to an extra or missing chromosome
Why are only certain aneuploidies observed?
- Most aneuploidies are not compatible with life, so will not be observed
- Also, some may result in mild/no symptoms, making them difficult to diagnose
Why do aneuploidies of the sex chromosomes tend to be less severe?
- Y-chromosome is non essential and contains only a small number of genes, so less genes affected
- Variation in X-chromosome is also well tolerated, due to the dosage compensation mechanism already present to normalise X-chromosome gene expression between males and females
What mode of inheritance is sickle cell anemia?
Autosomal recessive
What is the genetic cause of sickle cell anaemia?
A single base substitution mutation in the beta-haemoglobin gene; this is a missense substitution, changin glutamic acid (GAA) to valine (GTA)
Why are those with a sickle cell anaemia genesmore resistant to malaria?
The sickle-shaped red blood cells are less hospitable to the parasite
What happens in area where malaria is endemic with regard to SCA?
In areas where malaria is endemic, the selective advantage of the sickle cell allele in protecting against malaria outweighs its deleterious effects on health.
How do you calculate the degrees of freedom required for a Chi Squared test?
(number of rows - 1) x (number of columns - 1)
If the chi-squared value is greater than the critical value, what does this mean?
It means you can reject the null hypothesis and conclude there is a statistically significant difference between the data sets
Why do some pathogens/parasites evolve more quickly than their hosts?
They have much shorter life cycles than their hosts, and often exist in very large numbers
What is the ‘Red Queen Hypothesis’?
Organisms must constantly adapt and evolve just to maintain their relative fitness in a constantly changing environment.
What is the SRY gene?
The SRY gene is a gene on the Y chromosome that is responsible for initiating male development in mammals. It encodes for the SRY protein, which acts as a transcription factor, regulating the expression of other genes involved in male development
What are transcription factors?
Proteins that help regulate gene expression by turning specific genes “on” or “off”
At what point is human sex determined?
Humans ex is determined 6 weeks post fertilisation, when the SRY gene is first expressed (or not expressed in females)
What is the indifferent gonad?
Refers to the early stage of development when the gonad is undifferentiated and has the potential to develop into either a testis or an ovary, depending on the presence or absence of the SRY gene.
What do Sertoli cells secrete during the gonad development in males?
Sertoli cells secrete Anti-Mullerian Hormone (AMH)
What is the role of Anti-Mullerian hormone?
AMH promotes Leydig cells to differentiate in the developing gonad
What do Leydig cells produce?
The steroid hormone testosterone
What happens to the mullerian and wolffian duct in males?
The mullerian duct breaks down, the wolffian duct remains
Is the WNT4 gene active or inactive in male development of the gonads?
WNT4 is absent
What do Theca cells produce during the gonad development in females?
Theca cells produce steroid hormone pregesterone
What do Granulosa cells produce during the gonad development in females?
Estradiol/estrogen
What happens to the mullerian and wolffian duct in females?
The mullerian duct remains, the wolffian duct breaks down
Is the WNT4 gene active or inactive during gonad development in females?
Active
What is polyspermy?
Polyspermy is a phenomenon in which an egg cell is fertilized by more than one sperm
What mechanisms are used to prevent polyspermy?
- Cortical reaction
- Electrical block
What is the cortical reaction in preventing polyspermy?
After the first sperm has successfully penetrated the egg, cortical granules are released.
These granules release enzymes that modify the zona pellucida and create a “hardening” of the outer layer and destroy sperm receptors
What is the electrical block in preventing polyspermy?
As soon as the first sperm enters the egg, it causes a change in the electrical charge of the egg cell membrane.
This change creates an electrical block that repels additional sperm from binding to the egg.
What are the 3 germ layers formed as the blastula develops during gastrulation?
- Ectoderm
- Endoderm
- Mesoderm
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What does the ectoderm give rise to?
- The skin
- Nervous system
- Sensory organs.
What is the endoderm?
The innermost layer of the embryo
What does the endoderm give rise to?
- Lining of the digestive tract
- Respiratory tract
- Other internal organs.
What is the mesoderm?
The middle layer of the embryo
What does the mesoderm give rise to?
- Muscles
- Bones
- Blood vessels
- Other connective tissues.
What is the trophoblast?
The layer of cells that forms the outer layer of the blastocyst
What is the main role of the trophoblast?
Invading into the wall of the uterus, forming the placenta
What are the main functions of the placenta?
- Exchange of nutrients and waste products
- Immune response
- Hormone production
What is the tripoblastic embryo?
An embryonic stage in which is characterised by the presence of three primary germ layers: the endoderm, mesoderm, and ectoderm.
What did the Gurdon experiment demonstrate?
The ability of specialised cells to be reprogrammed into a pluripotent state.
What is morphogenesis?
The process by which cells organise themselves into specific structures
What is determination of a cell?
The point at which the cell becomes committed to becoming a specific cell type
What are homeotic genes also known as?
Hox genes
What are Hox genes?
Genes responsible for regulating the identity and placement of body parts.
They encode transcription factors that control the expression of genes involved in cell differentiation and tissue development
What are two possible phenotypic results of mutations in homeotic genes?
- Body features growing in the incorrect place (e.g. legs where head should be
- Body features not being expressed (e.g. missing leg) or being expressed more then they should (e.g. two heads)
