MENDELS 1st & 2nd LAW

5.2 InheritanceInheritance of Traits in HumansThe ABO blood group system is based on presence or absence of antigens A & BThe antigens is controlled by alleles A, B & OAllele A: produce antigen AAllele B: produce antigen BAllele O: does not produce any antigensDetermination of blood group

Example 1

Example 2

exerciseA man with blood group O marries a woman with blood group B.Explain with a genetic diagram, how is it possible for the couple to have a child with blood group O?What is the percentage of their first child having blood B?Rhesus factorRhesus Factor (Rh Factor)Referring to the antigen found on the surface membrane of some red blood cellsRhesus positive (Rh + )People who have Rhesus factorRhesus negative (Rh -)People who do not haveAllele for rhesus + is dominant to rhesus -

FatherRhesus positiveRh + Rh -MotherRhesus negativeRh Rh -XRh +Rh -Rh -Rh -Male gameteFemale gameteRh +Rh -Rh -Rh + Rh -Rh- Rh-Rh -Rh+ Rh-Rh- Rh-Rh+ Rh- : Rh- Rh-Rhesus positive : Rhesus negative1 : 1

Rhesus factor & PregnanciesMothers Rh factorFathers Rh factorBabys Rh factorPrecautionsRh +Rh +Rh +NoneRh -Rh - Rh -NoneRh +Rh -Could be Rh + or Rh -NoneRh -Rh +Could be Rh positive or Rh negativeRh immune globulin injections

UNDERSTANDING INHERITANCEDetermination of the sex of a childChromosomesTwo types of chromosomes:AutosomesSex chromosomes

SEXAUTOSOMESSEX CHROMOSOMESSOMATIC CELLMale 44 / 22 pairsXY44 + XYFemale44 / 22 pairsXX44 + XXDETERMINATION OF THE SEX OF A CHILD

SEX-LINKED disordersSex Linked Alleleslocated on the X chromosomes not involved in sex determination

Sex Linked AllelesMale only need to inherit only one copy of the allele to exhibit the traitFemale must inherit two copy of the allele to exhibit the traitDisorders :Color blindness Haemophilia

Color blindness

Colour Blindness The inability to differentiate between red & green colorCaused by a gene mutation that is located on the X chromosomeMore male than females are color blind because:Allele for colour blindness (b) is recessive to the normal alelle B & is linked to chromosome XParents : Gametes: F1 Generation: XB XBHomozygous normal femaleXb YColour blind maleXBXbYXB XbXB YFemale carries the color blindness geneNormal MaleParents : Gametes: F1 Generation: Xb XbColour blind femaleXB YNormalmaleXbXBYXB XbXb YFemale carries the color blindness geneFemale carrierXbXb YColour-blind maleXB XbColour-blind maleHaemophiliaHaemophiliaBlood disease caused by a lack of clotting factorsCaused by a recessive gene (h) found on the X chromosome of the human

Genotype & phenotype of haemophiliaSexGenotypePhenotypeFemaleXHXHNormal FemaleXHXhCarrierFemaleXhXhHaemophiliaMaleXHYNormal MaleXhYHaemophiliarevision

A gene carried at the X chromosomePs mother is a carrier carrying one recessive allele for colour blindness and one dominant allele for normal vision // Ps mother : XBXbPs father is normal carrying one dominant allele for normal vision in his X chromosome and none in his Y chromosome // Ps father : XBYP received the X chromosome carrying recessive allele from the mother and a Y chromosome from the father (causing him to be coour blind)P is XbY

Mother(XBXB)Father (XbY)XXBXBXbY(XBXb)(XBY)(XBXb)(XBY)Carrier FemaleNormal MaleSR

25%25%

autosome