BIOLOGY TERM 2 Y10

12. Compare the nuclear division processes of mitosis and meiosis.

MITOSIS is a nuclear division process that produces normal body cells during growth, repair and replacement. - daughter cells are diploid and genetically identical to each other and parent cell - cells divide once only - occurs in somatic cells - two daughter cells MEIOSIS is a nuclear division process that occurs during sex cell formation in the gonads (ovaries and testes). - daughter cells are haploid and not genetically identical to each other or parents - cells divide twice - occurs in gonads - four daughter cells

14. Explain how the gender of a baby is determined.

Biological gender in humans is determined by whether or not an individual inherits a Y chromosome from their father. If a person does inherit a Y chromosome then they will biologically be male.

2. Recall that sexual reproduction provides greater genetic variation in the offspring than asexual reproduction

In asexual reproduction, offspring show little variation of characteristics. In sexual reproduction, offspring show great variation.

15. Recall that individuals possess two copies of every gene (as they are found on homologous chromosomes) in every somatic cell.

Individuals possess two copies of every gene (as they are found on homologous chromosomes) in every somatic cell.

9. Recall what karyotypes are and why they are used.

Karyotype: An image that depicts the full complement of the chromosomes present in a cell (arranged from biggest to smallest) - Karyotypes can be used to determine gender (males contain the Y chromosome) - Karyotypes can also be used to reveal chromosomal mutations (resulting in an incorrect number of chromosomes in cells)

21. Interpret and analyse pedigree diagrams.

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10. Analyse human karyotypes.

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18. Relate allele combinations in genotypes to phenotypes.

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19. Use punnett squares to predict possible allele combinations in the offspring produced by specific genetic crosses (for both autosomal inheritance and sex (X) linked inheritance)

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11. Outline the process of and importance of DNA replication.

- cell copies entire genetic compliment (genome) by duplicating each chromosome to prep for cell division - chromosome duplication involves DNA replication - DNA that runs full length of each chromosome replicates producing 2 identical copies (sister chromatids) - two chromatids have matching identical copies of the original DNA molecule - centromere holds the two sister chromatids together - before replication, the original DNA molecule is composed of two complementary strands of DNA, each base being paired with its specific partner (AT GC) - first step in DNA replication involves 'unzipping' of this double helix - each original strand of the DNA molecule now serves as a template that directs the production of new complementary strands - DNA nucleotides floating free in the nucleus attach to specific sites along the template surface according to the base-pairing rules - by the end of DNA replication, two identical DNA molecules have been formed consisting of one 'old' strand and one 'new' strand - resulting molecules are identical to the original DNA molecule and to each other

6. Describe the structure of DNA.

A DNA molecule is a long, double stranded molecule that is coiled tightly to produce a double helix. Each strand of DNA is made up of repeating building blocks, called nucleotides. Nucleotides are made up of three parts: a sugar, a phosphate group and a nitrogenous base. Alternating sugar and phosphate groups form the "backbone" of the structure. Nitrogenous bases, which are attached to the sugar molecules, may vary. A DNA molecule is made up of two chains of nucleotides, bound together by hydrogen bonds. These bonds join the complementary nitrogenous base pairs. Matching of the nitrogenous bases is called "base-pairing".

1. Distinguish between asexual and sexual reproduction

ASEXUAL REPRODUCTION Asexual reproduction is the production of offspring without involving sex cells (gametes). - can be produced from single parent dividing into 2, or from a part of 1 parent growing into a new organism - offspring always have same characteristics as parents (clone) - if environment changes, population will have little genetic variation to cope and sections of population may die out - quite energy efficient as no energy is wasted finding a mate - produce large numbers of offspring very rapidly SEXUAL REPRODUCTION Sexual Reproduction involves the union of sex cells (gametes) to form a zygote (a single fertilized cell). - 2 major types of gametes: sperm and ova (single ovum) - organs which produce these gametes called gonads - male gonads are called testes which produce sperm (small tadpole-shaped cells that can swim) - female gonads are called ovaries which produce ova or eggs (large, round-shaped cells which cannot swim) - associated with gonads are other organs which aid in the transfer and development of the gametes, which together form the reproductive system - always have different characteristics to parents - has advantage in a changing environment (chance of some organisms surviving is greater) - energetically very expensive, parents use energy for e.g. finding/attracting mates, defending territory - for sexual reprod. to occur, parents must produce gametes and ensure they are brought together at the same time

8. State the relationship between DNA, genes and chromosomes.

Chromosomes are made from DNA. Genes are short sections of DNA.

5. Recall the meaning of the following terms - DNA, chromosome, genes, alleles, autosomes, sex chromosomes, haploid, diploid, somatic cell.

DNA: Deoxyribonucleic acid is a double helix shaped molecule composed of repeating subunits called nucleotides. It is the main chemical that makes up chromosomes. Chromosome: Long strands of DNA (and protein) that contain genes and are normally found in the nucleus of cells. Genes: Regions of DNA along a chromosome that code for specific traits (the production of specific proteins). Alleles: A form of a gene. Autosomes: Chromosomes that are not sex chromosomes. Sex chromosome: Chromosomes that determine gender (X and Y). Haploid: Containing one set of each chromosome. Diploid: Containing two sets of each chromosome. Somatic Cell: A normal body cell (not a sex cell).

17. Recall the meaning of the following terms: dominant allele, recessive allele, heterozygous, homozygous, genotype and phenotype.

Dominant allele - the allele that will always be expressed (it fully masks the expression of another allele) Recessive allele - the allele that is easily masked by a dominant allele Heterozygous - both alleles are different Homozygous - both alleles are the same Genotype - the symbolic representation of alleles present Phenotype - the visible effect of the allele combinations (e.g. brown eyes)

13. Recall that sex cells contain half the number of chromosomes as somatic cells

Sex cells are HAPLOID (half the amount of chromosomes as somatic cells) Somatic cells are DIPLOID

7. Recall the nitrogen bases and their complimentary pairs in DNA.

Thymine (T), adenine (A), guanine (G) and cytosine (C). T pairs only with A and G pairs only with C.

16. Recall that traits are passed from one generation to the next via genes in chromosomes inside sex cells.

Traits are passed from one generation to the next via genes in chromosomes inside sex cells (traits are inherited)

20. Recall that human ABO Blood grouping is ...

a special form of inheritance that involves both multiple alleles, (3 alleles rather than 2 alleles) and co-dominance

3. Recall the major parts (and the functions) of the human male and female reproductive systems

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4. Recall the meaning of the terms gamete, gonad, zygote, embryo, ovulation, menstruation, fertilisation

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