Class Notes (837,356)
Canada (510,242)
Biology (2,437)
BIOLOGY 1A03 (746)
Lecture 3

BIOLOGY 1A03 Lecture 3: THEME 5

7 Pages
Unlock Document

Rosa Da Silva

Module 3 – Sex Chromosomes and Linkage INHERITANCE OBSERVED IN FAMILY HISTORIES • Limitations to observing human inheritance traits include few offspring and ethical issues in asking people to breed simply for the purpose of the study • For this reason, a family tree/pedigree of family history is used to segregate a specific trait of interest HUMAN GENOME COUNT 23 pairs of chromosomes 3 billion base pairs of DNA per ell 20 000 protein/RNA-coding genes Alleles linked on a single chromosome must be able to become unlinked and recombine UNIT I: THE INHERITANCE OF GENES ON THE X CHROMOSOME SEX CHROMOSOMES • Most regions of the X and Y chromosomes are largely non-homologous, meaning almost none of the genes in X have counterparts in Y, and vice versa • Recombination between these two chromosomes cannot occur • Small regions at the tips of the X and Y chromosome allow pairing and segregation SEX-LINKED GENE: located on either chromosome whose expression of the phenotype depends on the sex of the individual Y CHROMOSOME COUNT X CHROMOSOME COUNT 78 genes on the chromosome 1100 genes (most unrelated 25 proteins encoded for to sex-determination) 12.5 sex-determining proteins RECESSIVE X-LINKED INHERITANCE OF RED/GREEN COLOUR-BLINDNESS • Women who are heterozygous for the trait will not show the phenotype, but are carriers • Those who are homozygous will experience symptoms of the disease HEMIZYGOUS: any male who inherits the allele from his mother will be colour-blind for he only has one X chromosome, and therefore one locus ISHIHARA COLOUR TEST: consists of a circle containing different colour dots with an internal dot pattern forming a number that is clearly visible with normal vision RED/GREEN COLOUR-BLINDNESS PUNNET SQUARE RECESSIVE X-LINKED INHERITANCE OF HAEMOPHILIA • Results from a mutation in a gene encoding for a protein required for blood clotting HAEMOPHILIA PUNNET SQUARE: QUEEN VICTORIA UNIT II: GENETIC LINKAGE LINKED GENES ON THE X-CHROMOSOME • Mendel's second law of inheritance states that two genes sort independently during gamete formation, but this is not always the case • The homologous pair of X chromosomes in females during prophase I has 155 million bp and contains 1100 genes • There is an annotation of genes on the p arm (short) and q arm (long) DYSTRIOHIN GENE: codes for a protein needed for muscle cell development HPRT1 GENE: when mutated, leads to severe cases of acute arthritis LINKED GENES: located close together on the same chromosome, and therefore tend to be inherited together, avoiding separate segregation (i.e. Colour-blindness + Haemophilia) RECOMBINATION OF HOMOLOGOUS CHROMOSOMES • The linkage between genes can be broken in prophase I/II, resulting in individual inheritance • As a result, some offspring may inherit only one of the genes due to these recombination events ALLELE RECOMBINA
More Less

Related notes for BIOLOGY 1A03

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.