tamilhoogl.blogg.se - Examples of dominant traits

There are four possible phenotypes in the offspring. For example Huntington's disease which affects the nerves. If a heterozygous person has children with a normal (homozygous recessive) person, each child has a 50% chance of inheriting the disease. Heterozygous individuals suffer from the disease. The only way someone can have the disease is if one of their parents has it (and one of their grandparents etc). Some genetic diseases are caused by a dominant gene. For example in cystic fibrosis if both parents are heterozygous, each child has a 25% chance of being born with cystic fibrosis. To predict how many offspring will have a particular genotype you use a Punnett square. Because the disease is recessive, it can skip several generations.Ĭarrier (has no symptoms but carries the recessive allele)Ĭystic fibrosis affects the lungs. If two carriers have children, each child has a 25% of being born with the disease. A Recessive allele only has an effect if you inherit two copies eg ff (cystic fibrosis). That means that it shows up in the phenotype whether you have one copy of it, or two copies. Monohybrid cross - only one trait is studied. Phenotype is the physical appearance eg carrier of cystic fibrosis. Mendelian Genetics Genotype is the genetic makeup of an individual eg Ff or FF. The main exception to this is identical twins, which come from the same fertilized egg, so are genetically identical. The sperm that fertilizes the egg is also picked at random, and this random fertilization means that in humans one pair of parents could theoretically produce almost 70 trillion different offspring. This produces over 8 million different types of sperm and egg. When the egg and sperm are formed by meiosis the alleles separate at random ( independent assortment). Mutations form different versions of a gene called alleles ( for example there are alleles for blond hair, brown hair, red hair, black hair). So you end up with homologous pairs of chromosomes.Ī mutation is a change in the DNA. When the sperm (with 23 chromosomes) fertilizes the egg (with 23 chromosomes) they form a zygote or fertilized egg that has 46 chromosomes. Genes are on chromosomesĪnd you inherit one set of chromosomes from each parent.

One form of a gene may be dominant over another form which is recessive and the dominant form would be expressed.BSC 1005 Chapter 6 notes Chapter 6 : Genetics Genetics is the study of inheritance.įirst studied by Gregor Mendel in 1850-1870 using peas.Ī gene is a section of DNA that carries instructions for making proteins.

When the sperm fertilizes the egg, the father’s genes (and chromosomes) join the mother’s, or both contribute to the genetic makeup of the offspring.

Gene pairs separate during meiosis and the formation of the sex cells along with the chromosomes.

Genes act in pairs, one from each parent.

Real examples: Sudden Cardiac Death of the Young/Long QT Syndrome (has a recessive and dominant form recessive is associated with profound deafness), Tuberous Sclerosis Complex, Marfan Syndrome, Neurofibromatosis and Polycystic Kidney Disease.

Homozygotes for the dominant condition have a more severe form of the condition.

If both parents possess the trait, but it is absent in any of their offspring, then the parents are both heterozygous (“carriers”) of the recessive allele.

The trait is present whenever the corresponding gene is present (generally).

If parents don’t have the trait, their children should not have the trait (except for situations of gene amplification).

If the trait is displayed in offspring, at least one parent must show the trait.

Traits do not skip generations (generally).

Males and females are equally likely to have the trait.

Patterns for Autosomal Dominant InheritanceĪfter filling in the genotypes for individuals in several family trees that exhibit this mode of inheritance, some patterns that can be noticed are: Shaded individuals will either have a genotype of “Rr” or “R-“ (“RR” or “Rr”, not enough information to determine). Use this knowledge and additional knowledge about how genes are passed from generation to generation to complete the remainder of the pedigree. When completing this pedigree with autosomal dominant inheritance, individuals that are non-shaded are expressing the recessive phenotype and have a genotype of “rr”. Autosomal Dominant Inheritance Blank Pedigree (PDF)Īutosomal Dominant Inheritance Example Pedigree Answers (PDF)