Year 10 Genetics

Where are chromosomes found?

in the nucleus of a cell

What is contained in a chromosome?

tightly packed DNA

What are homologous chromosomes?

pairs of chromosomes which share similar size, centromere location, banding pattern etc

What is the structure of a chromosome?

Chromosomes are DNA wrapped around proteins to form a bundle. Chromosomes have a constriction point called the centromere which divides the cell into two sections or arms, the short arm is the p arm and the long the q arm.

How many chromosomes does a human have?

46 chromosomes, 22 somatic pairs and 1 sex pairs

What are the sex chromosomes of a female?

XX

What are the sex chromosomes of a male?

XY

What is an autosome?

a type of chromosome that is not a sex cell

What is a karyotype?

An image of the complete set of chromosomes in a nucleus (they usually use white blood cells), which are arranged from largest to smallest, usually in homologous pairs.

What can a karyotype be used to determine and how?

the sex of the cell’s organism by presence of X or Y chromosomes and missing, extra or malformed chromosomes can indicate genetic issues

list some genetic issues

Down, Klinefelter, XYY, Edwards and Turner syndromes

What is DNA?

deoxyribonucleic acid (DNA) is a nucleic acid, consisting of nucleotides

What is a nucleotide?

a nucleotide is made up of three parts: a 5-carbon sugar called deoxyribose, a phosphate group, and a nitrogenous base (the phosphate and sugar make up the sides of the ladder and the nitrogenous bases make up the rungs of the ladder)

What are the nitrogenous bases? (describe the pairs in answer)

T (Thymine) always pairs with A (Adenine) and G (Guanine) always pairs with C (Cytosine)

What is mitosis? in your answer explain its purpose

the division of somatic cells from one parent cell into 2 genetically identical daughter cells, its purpose is growth and repair

What is meiosis?

The division of sex cells (gametes). The parent cells in this process are diploid (a cell with two sets of chromosomes), these diploids are split into four - the cell cycle phases are completed twice - different daughter cells (they are haploid cells, one set of chromosomes). The daughter cells in meiosis are genetically different to the parent cell.

What is a DNA mutation?

a change in the genetic sequence (can occur spontaneously or due to a mutagen) it leads to the production of a different protein or the early finish of a protein (can be an insertion, deletion, duplication or inversion)

What are the two different types of mutation?

a change in a single base pair (point) or a change in the whole amino acid sequence (frameshift)

What is insertion?

part of one chromosome is removed and added to second chromosome

What is deletion?

part of the chromosome is removed

What is duplication?

part of the chromosome is copied

What is inversion?

part of the chromosome is replaced in reverse order

What is chromosomal mutation?

a mutation that changes the structure of an individual chromosome, leading to imbalance involving only a part of a chromosome (can have an affect on many genes along the chromosome) can be duplication, deletion, inversion, insertion or translocation

What is translocation?

parts of the chromosome are exchanged

What are the consequences of mutation?

Beneficial – increases chances of organism surviving and reproducing so genetics are passed on.

Deleterious – may cause death of the organism, prevents genetics from being passed to next generation.

Neutral – doesn’t increase or decrease chances of genetics passing on, but these mutations generally accumulate in the gene pool and lead to variation in a population.

Describe dominant traits

dominant traits must be present in order for the trait to be displayed, but there can be one or two dominant alleles (eg: AA or Aa – homozygous or heterozygous), dominant alleles are shown with a capital letter

Describe recessive traits

recessive traits must have two alleles present for the trait to be displayed (aa), recessive traits are usually shown with a lower case letter

What is co-dominance?

both alleles are expressed completely (are equally dominant) and an additional phenotype is produced (eg: in AB blood type, both A and B phenotypes are fully expressed)

What is incomplete dominance?

a blend of both alleles appear in heterozygous individuals

What are pedigrees used for?

to show patterns of inheritance through generations of families

What is a gamete?

mature haploid male or female sex cell (sperm or egg)

What is the difference between haploid and diploid cells?

diploid cells are all somatic cells (they have 2 complete sets of chromosomes – 2n), haploid cells have half the number of chromosomes (sex cells in humans - n)

What is a carrier?

A “carrier” is heterozygous for a trait and generally carries the recessive allele but does not display the trait. They can pass the allele onto their offspring.

What do you need to remember about multiple alleles?

an allele is a form of a gene found on a certain point of a chromosome, blood types are the most common multiple alleles, an example of co-dominance

What is sex-linkage?

a type of allele dominance controlled by genes on the X or Y chromosome

What is incomplete dominance?

a type of allele dominance where a mix of the dominant and recessive alleles will appear

How do X-linked genes work?

Sex determination in humans depends on the Y chromosome, the X chromosome also has many genes not related to sex determination but the Y chromosome is smaller and often lacks the equivalent gene, so only the gene on the X chromosome is read in males. These are known as X-linked genes. (we represent genes found on sex chromosome, with the letter superscripted above the chromosome letter when we are predicting sex-linked traits.  Eg  X^BX^b  and X^BY^-)

What are the stages of mitosis or cell cycle?

PMAT prophase (nuclear membrane disappears and threads of DNA are coiled onto chromosomes), metaphase (chromosomes line up to be split), anaphase (the splitting of the chromosomes into chromatids), telophase (cell divides, membrane forms and chromosomes uncoil)

What are proteins made of?

amino acids (think of a long strand of beads being a protein and each bead is a different amino acid)

What are codons?

triplets of nucleotides – A, T, C or G), code for a specific amino acid

What is Down Syndrome?

extra copy of chromosome 21, also called Trisomy 21 (one of only a few trisomy disorders in which the child has high probability of living to adulthood, causes short stature, intellectual and developmental disability, reduced life span (prone to heart disordered) and characteristic physical features)

What is Klinefelter Syndrome?

Trisomy of the sex chromosomes XXY, sterile, low testosterone and taller than average

What is XYY Syndrome?

extra y chromosome

What is Edwards Syndrome?

extra chromosome 18 (trisomy 18)

What is Turner Syndrome?

missing 2^nd sex chromosome (this is the only monosomy in which the embryo survives, if any other chromosomes are missing then embryo/fetus does not survive, affected are: sterile, shorter than average, various other characteristic symptoms)

What is trisomy?

a condition in which an extra copy of a chromosome is present in the cell nuclei, causing developmental abnormalities