Sex Cells and Inheritance

Cells- more on the nucleus Animal and plant cells contain a nucleus. The nucleus controls cell activities including cell division. It also contains the genetic information needed to produce a new cell. The information is organized into units called genes. Our genes are on chromosomes

Unravelling a chromosome:                                                                Unravelling a chromosome: Access excellence

Chromosomes and Genes Chromosomes come in pairs. Human body cells have 23 pairs of chromosomes. This gives a diploid number of 46. Human gametes (sperm and egg cells) contain 23 chromosomes. This is the haploid number.

Reproduction Revision Pupil Activity Complete the following sentences Another name for sperm and egg cells is ________ These sex cells join to make one cell during __________ This cell grows into a baby by __________________ many times. Each body cell in the baby contains ____ pairs of chromosomes. One of the chromosomes in each pair comes from the _______, the other from the _______ gametes fertilization multiplying & dividing 23 mother father

Human Life Cycle Diploid Zygote 46 Haploid Sperm 23 Adult 46 Haploid Egg 23 fertilization

Genes A characteristic is controlled by the two forms of a gene present in an individual. (but the particular combinations are limited by the genetic makeup of your parents). The different forms of a gene are called alleles. ,.

Genetics Buzzwords Phenotype Genotype Allele Heterozygous Homozygous physical appearance of an organism. Phenotype the set of genes (alleles) that an organism possesses Genotype Allele different forms of the same gene when the two alleles are different Heterozygous when two alleles (gene types) are identical Homozygous

Dominant allele which controls the characteristic whenever it is present. BB or Bb recessive allele whose characteristics only show up when it is present on both chromosomes bb

Boy or Girl? The sex of a child is determined by specific chromosomes called X and Y chromosomes. In humans, each male gamete may have an X or a Y chromosome, while each female gamete has an X chromosome. Female Body cells are XX Male Body cells are XY All X X or Y gametes

Offspring: Male or female? X Y Mother XX X Father XY X Y gamete 1:1 ratio male to female offspring Offspring: Male or female? X Y XX XY This can also be shown and combinations worked out using a Punnett square:

Genes and Genotypes Genotype: set of genes that an organism possesses Each organism has two forms of the same gene -one inherited from mother -one inherited from father We can say that ‘Organisms possess two alleles for each different gene’

Genotypes and Symbols Each allele is represented by a letter -capital letter if the allele is dominant (A) -lower case letter if the allele is recessive (a) Each organism will have two letters -1 represents the allele it receives from its mother -1 represents the allele it receives from its father

Height in Pea Plants T = tall (dominant) t = short (recessive) A pea plant can be: TT = homozygous tall Tt = heterozygous tall (because T is dominant to t) tt = homozygous short

Gene combinations The simplest genetic cross involves one characteristic and is called a monohybrid cross. In this the parents (P) are crossed (bred) with each other, and the offspring (F1 generation) observed and counted. (Bred with) X Parents Phenotypes Genotypes Gametes Tall TT all T Dwarf tt all t Tt all tall F1 genotype F1 phenotype